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Unit 10. System Storage Overview What This Unit Is About This unit is an overview of AlX Version 4/5 system storage. What You Should Be Able to Do After completing this unit, you should be able to: Describe the terminology and the concepts associated with: Physical Volumes Volume Groups Logical Volumes Physical Partitions Logical Partitions Describe how file systems and logical volumes are related. How You Will Check Your Progress Accountability: Checkpoint questions • Exercises References AlX Version 4/5 System Management: Operating System and Devices AlX Storage Management 1

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Unit 10. System Storage Overview

What This Unit Is About

This unit is an overview of AlX Version 4/5 system storage.

What You Should Be Able to Do

After completing this unit, you should be able to:

• Describe the terminology and the concepts associated with:Physical Volumes Volume Groups Logical Volumes Physical Partitions Logical Partitions

• Describe how file systems and logical volumes are related.

How You Will Check Your Progress

Accountability:

• Checkpoint questions• Exercises

References

AlX Version 4/5 System Management: Operating System and Devices

AlX Storage Management

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Instructor Guide

Objectives

After completing this unit, students should be able to:

• Describe the terminology and concepts associated with:

-Physical Volumes

-Volume Groups

- Logical Volumes

- Physical Partitions

- Logical Partitions

• Describe how file systems and logical volumes arerelated.

Figure 10-1. Objectives

Notes:

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Instructor Guide

Components of AlX Version 4/5 Storage

• Files

• Directories

• File Systems

• Logical Storage

• Physical Storage

• Logical Volume Manager

Figure 10-2. Components of AlX Version 4/5 Storage

Notes:

These are the basic components or building blocks of AlX Version 4/5 storage. As a user you work with files and directories. As a system administrator you will work with the others as well.

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Instructor Notes:

Purpose — To provide a framework of discussion for the next three units.

Details — This is meant to provide a road map of what will be covered in depth over the next three units.

Additional Information —

Transition Statement — Before we discuss AlX Version 4/5 storage, let's look at how UNIX systems in general have traditionally handled disk storage.

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Instructor Guide

Traditional UNIX Disk Storage

PROBLEMS:

Fixed partitionsExpanding size of the partitionLimitation on size of a file system and a fileContiguous data requirementTime and effort required in planning ahead

Figure 10-3. Traditional UNIX Disk Storage

Notes:

Traditionally, disk partitioning has been implemented via partitions. Customers had to select the correct size for each partition before the system could be installed.

Each file system sits on a partition on the hard disk.

Changing the size of the partition and thus the file system is no easy task. It involves backing up the file system, removing the partition, creating new ones and restoring the file system.

A major limitation to partitions is that each partition has to consist of contiguous disk space. This characteristic limits the partition to reside on a single physical drive. It cannot span multiple physical volumes. Since file systems are always contained within a partition, no file system can be defined larger than the largest physical drive. This means that no single file can exist larger than the largest physical drive.

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Instructor Guide

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Instructor Notes:

Purpose — Define the problems of managing the storage space without the LVM.

Details — The foil highlights all the difficulties that can be incurred with other operating systems. We will discuss how the LVM handles all these problems in this session.

Transition Statement — AlX Version 4/5 has implemented something called the Logical Volume Manager designed to address the limitations of traditional UNIX storage. Let's see what the benefits are before delving into how it provides those benefits.

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Instructor Guide

Benefits of the LVM

• Logical volumes solve non-contiguous space problems

• Logical volumes can span disks

• Dynamically increase logical volume size

• Logical volumes can be mirrored

• Hard disks easily added to a system

• Logical volumes can be relocated

These tasks can be performed on a running system.

Most of the problems of disk space management have been changed from customer problems to logical volume solutions!

Figure 10-4. Benefits of the LVM

Notes:

In traditional UNIX implementations, customers had to select the correct size for each partition before the system could be installed. Each file system sat on a partition on the hard disk. Changing the size of a partition and thus the file system was no easy task. It involved backing up the file system, removing the partition, creating a new one, and restoring the file system.

Since a partition had to consist of contiguous space on a single device, it was possible that the process could be made even more difficult if other partitions had to be "moved", using the same process as described above, to make room for the new partition.

These problems have been virtually eliminated in AlX through the addition of the Logical Volume Manager.

Note that the tasks listed above can be performed while users are on the system.

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Instructor Notes:

Purpose — Describe the benefits of the Logical Volume Manager so students understand the important role it plays in AlX.

Details — Tell the students what the benefits are of the Logical Volume Manager and how it makes the life of the system administrator so much easier. If you have any stories you can share with students on the difference in time it takes to reorganize partitions and disk space in a traditional UNIX environment vs an AlX environment, do so. Real life experiences can really bring home the benefits the facility brings to UNIX.

Be sure to mention that the benefits listed on the graphic can all be accomplished while users are on the system!

Transition Statement — Let's begin our look at the Logical Volume Manager by seeing how physical disks are viewed by the operating system.

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Figure 10-5. Physical Storage

Notes:

Volume Group

A volume group is the largest unit of storage allocation under AlX. A volume group consists of a group of physical volumes (disks) all of which are accessed under one volume group name. The combined storage of all of the physical volumes can be allocated to a single object within the volume group.

A volume group (for example a number of externally connected SCSI disks) may be disconnected from one system and directly connected into another.

A volume group is manipulated as a collection of physical partitions which lie on the physical volumes within the volume group. The size of the physical partitions within a volume group is constant.

Physical Volumes

A physical volume is the name used to distinguish an actual disk within AlX Version 4. A physical volume may be either internally attached to the system or externally

Physical Storage

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Instructor Guide

attached. Before a physical volume can be used it must be added to an existing volume group or a new volume group must be set up for it.

When a physical volume is added to the system, a /dev/hdiskn device file is set up for it in the /dev directory. This file may be used to access the device directly, but this is not often done.

Physical Partitions

A physical partition is a division of a physical volume. It is the basic unit of disk space allocation in AlX Version 4/5.

All physical partitions within a volume group are the same size. The default size of the physical partitions in a volume group is 4MB. The default number of physical partitions per physical volume is 1016. Thus, a volume group that contains a physical volume larger than 4.064 gigabytes must have a physical partition size greater than 4 megabytes.

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Instructor Guide

Instructor Notes:

Purpose — Define the terms VG, PV and PP.

Details — Explain the foil, by also mentioning the following points:

• PVs have a naming convention of /dev/hdiskx where x is a number allocated by the operating system. It is usually the next available number.

• A PV can only belong to one VG.

• There can be many VGs defined on one system. These can be used to separate out the operating system from the application code, from the application data, etc. There can be up to 255 VGs per system.

• The default VG that contains the operating system is rootvg which is created by default.

• VGs can theoretically contain up to 32 PVs (although this is not a practical figure as far as administrative costs and performance goes). Also, as bigger disks have become more prevalent, this 32-disk limit is usually not achieved because the space in the VGDA is used up faster as it accounts for the capacity on the bigger disks. Large disks require more management-mapping space in the VGDA, causing the number and size of available disks that can be added to the existing volume group to shrink. When a disk is added to a volume group, not only does the new disk get a copy of the updated VGDA, but all existing drives in the volume group must be able to accept the new, updated VGDA.

The exception to the 32 PV/VG limit is rootvg. If one disk is used at install time for rootvg, then the maximum PVs for rootvg is 7. This maximum is incremented by one for each additional disk used at install time (i.e. 2 PVs for rootvg at install means a maximum of 8 PVs in rootvg, 3 used means a max of 9 and so on). This 'maximum' is actually referred to as a 'reference number' because it may be possible to add even more disks to rootvg, depending on the size and number of disks already defined for rootvg.

• The default PP size should not be changed, however if there is a need, then the PP size can be changed in increments of the power of 2 up to 256 MB each. AlX V4.3.1 also supports physical partition sizes of 512MB and 1024MB.

• The default limit for the number of physical partitions per physical volume is 1016. AlX provides support for multiples of 1016 PPs per PV, up to a maximum of 32512 PPs per PV. Be aware that if you choose to have more than 1016 PPs per PV, you will decrease the maximum number of physical volumes supported in the volume group. Details on this will be discussed in the next unit.

Transition Statement — We can group together a number of physical volumes into a volume group. Let's take a closer look at volume groups.

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You can:• Add new disks to rootvg• Create new volume groups as required

Why create new volume groups?• Separate user file systems from the operating file system• Disaster recovery• Data integrity and security• Data maintenance• Data portability

Figure 10-6. Volume Groups

Notes:

When the system is installed, the root volume group (rootvg) is created. This is where the AlX operating system files will be contained.

Additional disks can either be added to rootvg or a new volume group can be created for them.

If you have external disks, it is recommended that they be placed in a separate volume group. This will protect the operating system files in the event that any changes to, or movement of, these files should occur.

By maintaining the user file systems and the operating system files in distinct volume groups, the user files are not jeopardized during operating system updates, reinstallations, and crash recoveries.

Instructor Guide

Volume Groups

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Maintenance is easier because you can update or reinstall the operating system without having to restore user data.

For security, you can make the volume group unavailable using varyoffvg.

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Instructor Guide

Instructor Notes:

Purpose — Define the advantages of separate VGs.

Details — Discuss the main reasons for having external VGs as opposed to internal, and what considerations have to be made when adding a new disk to the system.

The rootvg includes paging space, the journal log, boot data and dump storage usually each in its own logical volume. The rootvg has attributes that differ from the user-created VGs. For example, it cannot be imported or exported (moved) like other VGs can.

Transition Statement — There is a portion of the disk which holds all the "administrative" information related to the VG in terms of the PVs and the LVs. It is called the Volume Group Descriptor Area (VGDA).

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Figure 10-7. Volume Group Descriptor Area

Notes:

VGDA The Volume Group Descriptor Area (VGDA) is an area of disk, at least one per PV, containing information for the entire VG. It contains administrative information about the volume group (for example, a list of all logical volume entries, a list of all the physical volume entries etc.). There is usually one VGDA per physical volume. The exceptions are when there is a volume group of either one or two disks (illustrated).

Quorum There must be a quorum of VGDAs available to activate the volume groupand make it available for use (varyon). A quorum of VGDA copies is needed to ensure the data integrity of management data that describes the logical and physical volumes in the volume group. A quorum is equal to 51% or more the VGDAs available.

A system administrator can force a volume group to varyon without a quorum. This is not recommended and should only be done in an emergency.

Volume Group Descriptor Area

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Instructor Guide

Instructor Notes:

Purpose — Define the purpose of the VGDA.

Details — The way the system determines if an entire VG is going to be activated or not is by checking the quorum for a particular VG. If more than 51 % of the VGDAs are good, then it will bring the VG on-line. If it also notices any backdated VGDAs, the LVM will update these too.

Make sure the students are clear that all VGDAs within a VG should be the same.

Out of the different configurations shown, the most dangerous one out of the three is the second one - having two disks in a volume group, because if the disk that contains the two VGDAs goes down, the quorum will be lost and the VG will be taken off line. However remember that many students probably have a two-disk setup, so try not to alarm them too much, and tell them that when/if they bring in another disk into their two disk VG, the environment will be far more stable.

Additional Information — In general, the VGDA can expand and take up as much space on the disk as is needed. This is true for all VGs except for the rootvg, whose VGDA size is set at installation time and cannot be changed. The VGDA is fixed at install time to allow it to fit into memory when booting. This is the reason why the rootvg can only be extended by a few disks after installation and the reason that rootvg should only contain the operating system.

It is also possible to have a non-quorum volume group. The purpose of these types of volume groups is to have data continuously available even when there is no quorum. This may be desirable in a two or three disk volume group where logical volumes are mirrored. Thus, if a disk failure occurs, the VG remains active as long as there is one logical volume copy intact on a disk. To initially activate a non-quorum volume group, all of the volume group's physical volumes must be accessible or the activation fails. Because non-quorum volume groups stay online until the last disk becomes inaccessible, it is necessary to have each disk accessible at activation time. This information is being placed in the 'Additional Information' section since we have not yet introduced the concept of logical volumes and mirroring.

Transition Statement — Now that we have seen the "physical" side of the LVM let's take a look at the "logical" side.

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Figure 10-8. Logical Storage

Notes:

A physical partition is the smallest unit of allocation of disk. Each logical partition maps to a physical partition which physically stores the data.

Obviously, the logical partitions within a volume group are the same size as the physical partitions within that volume group.

A logical volume consists of one or more logical partitions within a volume group.

Logical volumes may span physical volumes if the volume group consists of more than one physical volume. Logical volumes do not need to be contiguous within a physical volume because the logical partitions within the logical volume are maintained to be contiguous. The view the system sees is the logical one. Thus, 1 physical partitions they point to can reside anywhere on the physical volumes in the volume group.

Logical volumes may be increased in size at any time, assuming that there are sufficient free physical partitions within the volume group. This can be done dynamically through SMIT even when users are doing work in that logical volume.

Instructor Guide

Logical Storage

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Instructor Guide

However, logical volumes cannot easily be decreased and require a file system backup and restore to a recreated smaller logical volume.

Logical volumes consist of a number of logical partitions, so when a logical volume is being created the size requested is increased to the next logical partition boundary. Typically, the logical/physical partition size is 4MB so a logical volume will be a multiple of 4MB in size. Logical/physical partition sizes range from 1MB - 256MB. AlX also supports logical/physical partition sizes of 512MB and 1024MB.

A volume group is where the physical and logical views of storage meet. It is both a physical view and a logical view.

Table 10-1. Limitations for Logical Storage Management

Volume group 255 per system

Physical volume Up to 32 per volume group

Physical partition 1016 per physical volume, up to 256MBeach in size

Physical partitions in AlX Multiples of 1016 per physical volume,up to 32512 PPs per PV. PP sizes of

512MB and 1024MB are also supported.

Logical volume 256 per volume group

Logical partition 32,512 per logical volume

The Logical Volume Manager (LVM) consists of the logical volume device driver (LVDD) and the LVM subroutine interface library. The LVM controls disk resources by mapping data between a more simple and flexible logical view of storage space and the actual physical disks. The LVM does this using a layer of device driver code that runs above traditional disk device drivers.

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Instructor Guide

Instructor Notes:

Purpose — Define the terms LV and LP.

Details — Define the terms in connection with the physical side of things. Also point out:

• Data can be placed on any disk/partition within the VG. This will obviously cause fragmentation, as there are no restrictions as to where the data should be placed. The operating system needs to have a contiguous view of all the data and so it creates LVs.

• The naming convention used for system defined LVs is /dev/hdx and for user created LVs (if a name is not specified) is /dev/lvxx.

• An LV can only contain one file system. Although we have not defined file systems yet, it is important to mention this here and warn the students that there will be more on file systems coming up. It is very important to establish a clear relationship between an LV and a file system and to stress that these go hand in hand.

• A LP is always as big as a PP.

More details on the AlX physical partition enhancements will be covered in the next unit.

Transition Statement — Now you know what a logical volume is, how are they used?

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Uses of Logical Volumes

A logical volume may contain:

• Journaled file system (for example: /dev/hd4)

• Paging space (/dev/hd6)

• Journal log (/dev/hd8)

• Boot Logical Volume (/dev/hd5)

• Nothing (raw device)

Figure 10-9. Uses of Logical Volumes

Notes:

When you install the system, you automatically create one volume group (rootvg) which consists of a base set of logical volumes required to start the system. rootvg, contains such things as paging space, the journal log, and boot data, each usually in its own separate logical volume.

You can create additional logical volumes with the mklv command or go through the SMIT menus. This command allows you to specify the name of the logical volume and to define its characteristics.

The theoretical maximum number of user-defined logical volumes per volume group is 255, but the true limit is determined by the total size of the combined physical volumes assigned to the volume group.

The native file system on AlX Version 4 is the journaled file system. It uses database journaling techniques to maintain consistency. It is through the file system's directory structure that users get access to files, commands, applications, etc.

Paging space is fixed disk storage for information that is resident in virtual memory but is not currently being accessed.

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Instructor Guide

The journal log is the logical volume where changes made to the file system structure are written until such time as the structures are updated on disk. Journaled file systems will be discussed in greater detail later in the course.

The boot logical volume is a physically contiguous area on the disk which contains the boot image.

A raw device is simply an empty logical volume. Sometimes an application, for example a database package, may require a raw device.

When you install the operating system, the dump device is automatically configured for you. By default, the primary device is /dev/hd6, which is the paging logical volume, and the secondary device is /dev/sysdumpnull. For systems migrated from versions of AlX earlier than 4.1, the primary dump device is what it formerly was, /dev/hd7.

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Instructor Notes:

Purpose — Define the uses of LVs.

Details — LVs can contain a number of different types of entities, the most common one being the journaled file system.

Encourage the students to recognize standard system-defined LV names. For example, /dev/hd6 will always contain one of the paging spaces.

Do not explain in detail each of the named LVs.

This foil is meant to be a transition to an overview of the file system. What you are trying to accomplish is to show the connection between a logical volume and a file system early in the storage discussion. Once students see this connection, the rest of the concepts should make more sense to them.

Discussion Items - Ask if anyone has set up raw LVs and if so for what?

Raw LVs are usually used by databases which require empty devices for them to place and manage the data on. Databases usually use their own file system structures and do not use an AlX file system.

Transition Statement — The most common use for a logical volume is as a file system. Let's see what that is.

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Instructor Guide

What Is a File System?

• A file system is:

-Method of storing data

- Hierarchy of directories

•Three types supported:

- Journaled File System (jfs) -

CD-ROM File System (cdrfs)

- Network File System (nfs)

• Different file systems are connected together viadirectories to form the view of files users see.

Figure 10-10. What is a File System?

Notes:

AlX supports 3 native file system types:

jfs Journaled File System which exists within a Logical Volume on diskcdrfs CD-ROM File System on a Compact Discnfs Network File System accessed across a network

Although these are physically different, they appear the same to users and applications.

A file system is a directory hierarchy for storing files. It has a root directory and subdirectories. In an AlX system, the various file systems are joined together so that they appear as a single file tree with one root. Many file systems of each type can be created.

Because the available storage is divided into multiple file systems, data in one file system could be on a different area of the disk than data of another file system. Because file systems are of a fixed size, "file system full" errors can occur when that file system has become full. Free space in one file system cannot automatically be used by an alternate file system that resides on the same physical volume.

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Instructor Guide

Instructor Notes:

Purpose — Define what a file system is.

Details — You can have many different file systems connected under the hierarchical tree. However, from an end user's point of view, everything looks the same.

The student should be familiar with the concept of files and directories, so to tie file systems into their understanding, you could use the following board work:

You can present the diagram in the following way:

A group of files are placed in a directory, a group of directories are placed in a file system: a file system must sit on a logical volume, and a group of logical volumes all exist under one volume group. We will consider later on, the benefits of having file systems.

Typically the students will be using journaled file systems, which is the default type of file system for AlX. We will consider jounaling a little later on. But these are files that exist on your local disks. However, there is a feature where remote file systems can also be made to appear as if they belong and sit on your local disks, this being network file systems. We will not be considering NFS in this course.

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Instructor Guide

Why Have File Systems

• Can strategically place it on disk for improved performance

• Some tasks are performed more efficiently on a file system than on each directory within the file system. For example: back up, move, secure an entire file system

• Can limit disk usage of users by file system (quotas)

• Maintain integrity of the entire file system structure. For example: if one file system is corrupted, the others are not affected

• Special security situations

• Organize data and programs into groups for ease of file management and better performance

Figure 10-11. Why Have File Systems

Notes:

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Instructor Notes:

Purpose — Describe the benefits of file systems.

Details — A file system is an entity that you can control for performance reasons by moving it to a specific place on the disk. This is possible because a file system sits on an LV, which in turn can be placed anywhere on the disk. Also, for security reasons you can unmount (make unaccessible) the data at specific times.

Limits can also be set on a per file system basis, limiting users on the amount of disk space available to them. This will be discussed in a later unit.

Integrity checks can be carried out on a per file system basis, which again will be dealt with in a later unit.

Transition Statement — Let's look at the standard file systems in AlX Version 4/5.

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NOTE: The drawing depicts logical not physical devices

Figure 10-12. Standard File Systems in AlX

Notes:

When AlX Version 4/5 is first installed on a stand alone system there will be only five journaled file systems in existence:

• / (root) = /dev/hd4

Instructor Guide

Standard File Systems in AlX

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At the top of the hierarchical file tree. It contains the files and directories critical for system operations including the device directory and programs that complete the boot process.

• /usr = /dev/hd2Operating system commands, libraries and application programs. Can be shared across the network.

• /var = /dev/hd9varVariable spool and log files. The files in this file system vary considerably depending on system activity.

• /home = /dev/hd1Users' home directories (was /u in earlier versions of AlX). This is traditionally where user data files are stored.

/tmp = /dev/hd3

Space accessible to all users for temporary files and work space. Should be cleared out frequently.

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Instructor Guide

/etc/filesystems

/:dev = /dev/hd4vol = rootmount = automaticcheck = falsevfs log

= jfs= /dev/hd8

type = bootfs

/home:dev = /dev/hd1vol = "/home"mount = truecheck = truevfs log

= jfs= /dev/hd8

/home/john:dev

= /dev/lv00

vfs log

= jfs= /dev/hd8

mount = truecheck = trueoptions = rw

Figure 10-13. /etc/filesystems

Notes:

The /etc/filesystems file documents the layout characteristics, or attributes, of file systems. It is in a stanza format which means a resource is named followed by a colon and a listing of its attributes in the form of attributes = value.

Each stanza in the /etc/filesystems file names the directory where the file system is normally mounted.

The file system attributes specify all the parameters of the file system. They are as follows:

check used by the fsck command to determine the default file systems to be checked. True enables checking

dev for local mounts identifies either the block special file where the file systemresides, or the file or directory to be mounted

mount used by the mount command to determine whether a file system should be mounted by default

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Instructor Guide

Possible values are:

automatic file system mounted automatically at system startup

true file system mounted by the mount all command. Thiscommand is issued during system initialization to automatically mount such file systems

false file system will not be automatically mounted

type used to group together related file systems which can all be mounted with the mount -t command

vfs specifies the type of mount. For example, vfs = nfs

vol used by the mkfs command when initiating the label on a new file system

log the device to which log data is written, as this file system is modified. (Thisoption is only valid for journaled file systems)

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Instructor Guide

Instructor Notes:

Purpose — Describe the contents of the /etc/filesystems file.

Details — The /etc/filesystems file serves two purposes:

• Documents the layout characteristics of the file system

• Frees the person who sets up the file system from having to enter and remember items such as the device where the file system resides, because the information is defined in this file

Each stanza names the directory where the file system is normally mounted.

Additional Information — UNIX system administrators who are familiar with other flavors of UNIX may wish to compare this file to /etc/fstab or /etc/vfstab.

Transition Statement — In the /etc/filesystems file the term "mount" is used. What is mounting?

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Instructor Guide

Mount

mount: the glue that logically connects filesystems to the directory hierarchy.

File systems are associated with devices represented by special files in /dev - the logical volume.

When a file system is mounted, the logical volume and its contents are connected to a directory in the hierarchical tree structure.

Example:# mount /dev/lv00 /home/patsie

Figure 10-14. Mount

Notes:

A file system has to be mounted in order for it to be available for use. Use the mount command or SMIT to do this. The file system can also be umounted using the umount or unmount command, or SMIT. These commands can be executed by either the root user or a member of the system group.

Full path names must be used when specifying the mount point.

It is possible to have file systems automatically mounted at boot time. This can be specified in the /etc/filesystems file using the mount = automatic or mount=trueparameters.

If SMIT is used to create the file system, the mount point is created automatically.

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Instructor Guide

Instructor Notes:

Purpose — To describe what mounting is.

Details — The process of mounting is a key piece to understanding how the individual file systems are joined to form the view of the system the user sees. A file system has to be mounted in order for it to be available for use.

The mount command has many options. The graphic shows an example of this command. In the example, /dev/lv00 is the logical volume and /home/patsie is the mount point. This is the mount point that we will use in the examples on the next two pages. The mount point is always a directory and it should be empty.

Transition Statement — Let's look at the directory tree structure before and after a file system is mounted.

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Mounting Over an Empty Directory

Figure 10-15. Mounting Over an Empty Directory

Notes:

In order for users to get access to the data contained in a file system, it must be mounted. When the file system is mounted, it becomes a part of the hierarchical tree structure of files and directories. From the users perspective, there is no way to tell where one file system ends and another begins.

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Instructor Notes:

Purpose — Show how file systems are connected to form a single view to users.

Details — Discuss how even though each file system is a separate entity, they are connected together via the mount point directories so that the system of files and directories are seen as one large file system to end users.

In the example shown, /home/patsie is the mount point. Again, mention that the mount point must be a directory and it should be empty. The next page will illustrate what happens if the mount point is not empty.

Transition Statement — Since file systems can be mounted on a directory which has the required permissions, they can be "mounted over" directories that have files in them. Let's see what happens if you do this.

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Instructor Guide

Mounting over Files

Figure 10-16. Mounting Over Files

Notes:

It is possible to mount "over" files and sub-directories. The result is that the files and sub-directories that have been mounted over are now "hidden" from the users, i.e., inaccessible. They have not been lost though. They will again be accessible when the unmount command has been executed on the covering file system.

Not everyone has the authority to mount file systems randomly. Authority is based on two things: what the default mount point is, as specified in the file /etc/filesystems, and whether the user has write authority to that mount point. Users can issue file or directory mounts provided they belong to the system group and have write access to the mount point. root can mount anywhere under any set of permissions.

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Instructor Guide

Instructor Notes:

Purpose — Show that file systems can be mounted over existing files and directories.

Details — Simply show students how this can happen and stress that the files don't go anywhere, they are still there. They simply can't be accessed while the file system is mounted over the directory that contains the files.

Transition Statement — How can you tell what file systems are on the system?

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Instructor Guide

Listing File Systems

# lsfs

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Name Nodename Mount Pt VFS Size Options Auto

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Figure 10-17. Listing File Systems

Notes:

You can list the various file systems that are defined using the Isfs command. This command will display information from /etc/filesystems and from the logical volumes in a more readable format.

Isfs will also display information about CD-ROM file systems and remote NFS file systems.

Isfs [-q] [ -c | -I ] [ -v vfstype | -u mountgrp ] [file system]

The data may be presented in line and colon (-c) or stanza (-l) format. It is possible to list only the file systems of a particular virtual file system type (-v), or within a particular mount group (-u). The -q option queries the superblock for the fragment size information, compression algorithm and the number of bytes per inode.

The SMIT fastpath to get to the screen which will accomplish the same task as the Isfs command is: # smit fs. The fastpath using the Web-based System Manager is wsm fs.

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Instructor Guide

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Instructor Notes:

Purpose — List all the file systems defined on the system.

Details — The information displayed is as follows:

the device (LV or CD-ROM) or remote directory name

(NFS only) the remote system name

the directory which is the mount point

virtual file system type: jfs = journaled file system cdrfs = CD-ROM, nfs = network file system

size in 512 byte blocks (data is allocated in 4KB clusters)

mount options, 'options' attribute in /etc/filesystems

mount at system startup,'mount' attribute in /etc/filesystems

Name

Nodename

Mount Pt

VFS

Size

Options

Auto

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Please note that if the Isfs command is executed, the output of the command will be slightly different as accounting information is also shown. This has been deliberately left out so that the foil is easier to read.

Transition Statement — Let's see how we can list all the logical volumes on a system.

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Listing Logical Volume Information_________

• List all Logical Volumes by Volume Group:# Isvg -I rootvg

LVNAME TYPE LPs PPs PVs LV STATE MOUNT POINT

Figure 10-18. Listing Logical Volume Information

Notes:

Isvg -I rootvg

Provides information about the logical volumes in the 'rootvg' volume group.

Islv Ivname

This provides status information about the selected logical volume within the volume group. For example, Islv hd6

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Instructor Notes:

Purpose — List the attributes of a logical volume.

Details — Do not spend too much time going through all the attributes. This will be covered in more detail in the next unit

Transition Statement — Before summarizing let's do a few review exercises.

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Instructor Guide

Unit 10 Checkpoint

1. How many different PP sizes can be set within a single VG?

2. By default, how big are PPs?

3. How many VGs can a PV belong to?a. Depends on what you specify through SMITb. Only onec. As many VGs as exist on the system

4. True or false? All VGDA information on your system is identical, regardless ofhow many VGs exist.

Using the output listing the file systems shown below, answer the questions on thenext page:

# lsfs

Name Nodename Mount Pt VFS Size Options Auto

/dev/hd4 — / jfs 8192 — yes

/dev/hd1 — /home jfs 90112 — yes/dev/hd2 — /usr jfs 507904 — yes/dev/hd9var — /var jfs 8192 — yes/dev/hd3 — /tmp jfs 16384 - yes/dev/cd0 — /infocd cdrfs ro yes/dev/lv00 -- /home/john jfs 8192 rw yes

Figure 10-19. Unit 10 - Checkpoint

Notes:

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Instructor Guide

Instructor Notes:

Details —

1. How many different PP sizes can be set within a single VG?

— Correct Answer

1. Only 1. By default, the value is 4MB

2. By default, how big are PPs?

— Correct Answer

2. By default 4MB

3. How many VGs can a PV belong to?

a. Depends on what you specify through SMITb. Only onec. As many VGs as exist on the system

— Correct Answer

3. b

T F 4. All VGDA information on your system is identical, regardless of how many VGs exist.

— Correct Answer

4. False

All VGDAs within a VG are the same.

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Instructor Guide

Unit 10 Checkpoint (Cont)

5. With which logical volume is the /home file system associated?

6. What type of file systems are being displayed?

7. What is the mount point for the file system located on the /dev/lv00 logical volume?

8. Which are the system supplied logical volumes and their associated file systems?

9. Which file system is used primarily to hold user data and home directories?

Figure 10-20. Unit 10 - Checkpoint (cont)

Notes:

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Instructor Guide

Instructor Notes:

Details —

Using the output listing the file systems shown below, answer the following question: # lsfs

Name Nodename Mount Pt VFS Size Options Auto

Using the output listing of logical systems above, answer the following question: 1. With which logical volume is the /home file system associated?

— Correct Answer

1. /dev/hd1

2. What type of file systems are being displayed?

----Correct Answer

2. Journaled file systems (jfs) and CD-ROM (cdrfs)

3. What is the mount point for the file system located on the /dev/lv00 logical volume?

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Instructor Guide

Correct Answer

3. /home/john

4. Which are the system supplied logical volumes and their associated file systems?— Correct Answer

4. /dev/hd4 /

/dev/hd1 /home

/dev/hd2 /usr

/dev/hd9var /var

/dev/hd3 /tmp

5. Which file system is used primarily to hold user data and home directories?

— Correct Answer------------------------------------------------------------------------------------------------

5. /home

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Unit 10 Checkpoint (Cont)# Isvg -I rootvg

LVNAME TYPE LPs PPs PVs LV State MOUNT POINT

hd6hd5hd8hd9varhd3Iv00

pagingbootjfslogjfsjfsjfs

81 11 21

8 1 1 1 2 1

1 open/syncd1 closed/syncd 1 open/syncd 1 open/syncd 1 open/syncd 1 closed/syncd

N/AN/AN/A/var/tmp/home/john

Using the output listing of logical systems above, answer the following question:

10. Which of the logical volumes above are examples of logical volumes with file systems on them?

Figure 10-21. Unit 10 - Checkpoint (cont)

Notes:

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Instructor Guide

Instructor Notes:

Details -

# Isvg -l rootvg

LVNAME TYPE LPs PPs PVs LV State MOUNT POINT

hd6 paging 8 8 1 open/syncd N/A

hd5 boot 1 1 1 closed/syncd N/A

hd8 jfslog 1 1 1 open/syncd N/A

hd9varhd3Iv00

jfsjfs jfs

1 21

1 21

11 1

open/syncd open/syncd closed/syncd

/var/tmp/home/john

1. Which of the logical volumes above are examples of logical volumes with file systems on them?

Correct Answer

1. hd9var, hd3, Iv00

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Instrucor Guide

Unit Summary

• The LVM is organized as follows:• A VG consists of one or more PV(s)• Each PV is divided into PPs• A LV is made up of LPs• LPs are mapped to PPs (usually on a 1 for 1 basis)

• Logical Volumes are used to contain:Journaled File Systems Paging SpacesDump Space Journaled LogBoot Logical Volume Nothing

• The most common use of logical volumes is to contain ajournaled file system.

Figure 10-22. Unit Summary

Notes:

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