Storage VirtualizationStorage Virtualization

Sisimon Soman

Study by IDC/EMC

• By 2010 nearly 1000 Exabytes (equal to 1000 billion Gigabytes) of digital information will created.

• If printed on paper, we can wrap earth 16 times using that paper.

• The total amount of digital information doubles in 18 months.

Numbers collected from EMC.com which is available for public

Types of Storage

• Classify into three according to the access mechanism between server and storage.– Direct Attached Storage (DAS)– Network Attached Storage (NAS)– Storage Area Network (SAN)

Direct Attached Storage (DAS)

• Disk(s) directly connected to the machine.• Most simple/common storage.• Example: Our Laptops, Desk tops etc

SCSI

Network Attached Storage

• Uses CIFS/NFS protocol to access files.• Similar to a remote shared folder.• Client side redirector forward the file requests to

NAS box.• Example: EMC Celerra, NetApp FAS

LAN LAN

Servers

NAS box

NAS - Module diagramApplication

File System Redirector

CIFS Protocol Layer

TCP/IP Stack

NIC Driver

User Space

Kernel Space

LAN LAN

CIFS Protocol Layer

TCP/IP Stack

NIC Driver

File System

Volume Manager

Disk Driver

NAS Box

Server

What is a SAN

Picture taken from wikipedia

EMC Symmetrix DMX 2000 EMC Symmetrix DMX 1000

SAN Continued..

• Example : EMC Symmetrix, CLARiiON

Fibre Channel Switch

Servers

SAN

SAN Architecture

Fibre Channel Switch

Controllers/Storage Processors (It can be ACTIVE-ACTIVE or ACTIVE-PASSIVE)

Disks

GBs of memory in each controller

Difference between SAN and NAS

• In NAS ‘file streams’ are transferred thru wire.

• In SAN ‘disk blocks’ are read from storage.• In SAN Fibre Channel is the common

communication mechanism. (SAN support SCSI over TCP/IP also, which is called iSCSI)

• In NAS file streams transfer over TCP/IP stack.

Common features of SAN

• Backup

• Replication

• Snapshot

• Features specific to SAN like SRDF for Symmetrix

SAN Specific data collected from wikipedia

Storage Virtualization - Advantages

• Hide the internal complexity of storage system.

• Better Disk block usage – Study shows only 30-40% of disk space is used effectively.

• Better Performance.

• Scalability.

Taxonomy of Storage Virtualization

• Virtualization at Host Operating system storage stack.

• Switch/Appliance based Virtualization.

• Virtualization at external storage array (SAN).

Storage Stack

File System

Volume Manager

Disk Class Driver

Hardware Driver

ApplicationUser Space

Kernel Space

Host Operating system Storage stack

Fibre channel adapter

Fibre channel Switch

SAN

Fibre Channel cable

Virtualization at Operating Storage Stack

File System

Volume Manager

Disk Class Driver

Hardware Driver

• A typical Windows Storage stack (Not much difference in Linux flavor)

IO Request flow thru each layer

Virtualization at File System Layer

File System

Volume Manager

Disk Class Driver

Hardware Driver

File1.doc

Disk blocks

Virtual Cluster Number (VCN)

Logical Cluster Number (LCN)

• NTFS expose IOCTL FSCTL_GET_RETRIEVAL_POINTERS, so that any app can query VCN-LCN mapping. Usually the disk defragment app uses this IOCTL.

HSM File System (Tiered Storage)

RAM ($50/MB)

SAN ($.5/MB)

TAPE($.05/MB)

Only 20-30% of actively used data

• Ex: EMC DiskXtender

Virtualization at Volume Manager- Spanned Volume

• Spanned Volume – Volume D is total 100MB which is spanned over Disk 1 and 2. Volume Manager adjust the physical address accordingly.

• NTFS support expanding the volume dynamically, its block allocation information (bitmap) is just another file and which can expand. FAT cannot expand volume without formatting the data.

Virtualization at Volume Manager - Striped Volume (RAID 0)

• Less latency time – Multiple disk simultaneously read/write small block of data to complete one read/write request.

Striped Volume

Virtualization at Volume Manager - RAID 5

• Also know as Striped Volume with parity.• Fault tolerance is achieved by reserving an equivalent of

one disk for keeping parity information.• Rotate the parity stripe to all disks - Avoid the possibility

of parity disk become busy all time.

RAID 5

Virtualization at Disk Controller

• Disk Controller convert Logical Block Address to Cylinder Head Sector address.

• Disk controller take care of damaged sectors also.

LBA 1

LBA 2

LBA 3

LBA 4

LBA 5

LBA n

Putting it all together

Windows Storage Stack

Switch based Virtualization

• Combine LUNs from one or more Arrays to a single virtual LUN and pass to host OS.

• Take one big LUN from one Array, divide it and give to different host OS.

• Security – One host can see certain LUNs only.• Vendors are adding more intelligence in switch

level like advanced volume management, caching, QoS functions…

• EMC Invista, IBM SAN Volume Controller

Switch level Virtualization

IBM EMC HP HDX

Intelligent switch – Virtualize LUNs from different array

Virtualization at SAN

Virtual Disk

Disk in the storage array

Questions ?Questions ?