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Physical StorageManagement
Module 6
Data ONTAP 7.3 Fundamentals
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Module Objectives
By the end of this module, you should be able to:
Describe Data ONTAP RAID technology
Identify a disk in a disk shelf based on its ID
Execute commands to determine disk ID
Identify a hot-spare disk in an FAS system
Calculate usable disk space
Describe the effects of using multiple disk
types
Execute aggregate commands in Data ONTAP
Define and create an aggregate
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Disks
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Disks
All data is stored on disks
To understand how physical media is
managed in your storage system, we will
address:
Disk types Disk qualification
Disk ownership
Spare disks
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Supported Disk Topologies
FC-AL
FAS2000 FAS3000 FAS6000
SATA
FAS2000 FAS3000 FAS6000 R200
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Disk Qualification
Use only NetApp Qualified Disks Modifying the DiskQualification Requirement
file can cause your
storage system to halt.
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Disk Ownership
Disks must be assigned to (owned by) a
controller.
Software Disk Ownership Hardware Disk Ownership
Ownership is assigned
FAS270
FAS3000 series
FAS2000 series
FAS6000 series
Ownership is based on slot used
R200
FAS250
FAS3000 series
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system> sysconfig -r
Volume vol0 (online, normal) (block checksums)Plex /vol0/plex0 (online, normal, active)
RAID group /vol0/plex0/rg0 (normal)
RAID Disk Device HA SHELF BAY CHAN Used (M...
parity 3a.16 4a 1 0 FC:A 17000/...
data 3b.17 4a 1 1 FC:A 17000/...
Disk Ownership
Disk ID = Loop_id.Device_id
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Disk Ownership: Loop_id
The loop_id is the designation
for the slot and port where anadapter is located. In the
following illustration, the loop_id
is 3b.
PROPERLYSHUTD OWNSYSTEMBEFOREOPENINGCHASSIS.
PCI 1 PCI 3
PCI 4PCI 2
DISCONNECTAC POWER
CORDBEFOREREMOVAL
I
O
AC
status
DISCONNECTAC POWER
CORDBEFOREREMOVAL
I
O
AC
status
Console
Console
0a 0b
0a 0b
F C
F C
e0a
e0a e0b
e0b RLM
RLM
e0c
e0c e0d
e0d
0d
0d0c
0c
F C
F C
0e
0e
LVDSCSI
LVDSCSI
L
I
N
K
L
I
N
K
L
I
N
K
L
I
N
K
L
I
N
K
L
I
N
K
L
I
N
K
L
I
N
K
3b
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Disk Ownership: Device_id
Shelf ID Bay Number Device ID
1 130 2916
2 130 4532
3 130 61484 130 7764
5 130 9380
6 130 10996
7 130 125112
Shelf ID
12345678910111213 Bay Number0
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The fcstat device_map Command
Use the fcstat command to troubleshoot
disks and shelves.
Use the fcstat device_map command to
show disks and their relative physical position
map of drives on an FC loop.
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Matching Disk Speeds
When creating an aggregate or traditional
volume, Data ONTAP selects disks:
With same speed
That match speed of existing disks
Data ONTAP verifies that adequate spares areavailable
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Using Multiple Disk Types in an Aggregate
Drives in an aggregate can be:
Different speeds
On the same shelf or on different
shelves
Avoid mixing drive types within an
aggregate
The spares pool is global1 2
3 4 5 6
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system> disk zero spares
Spare Disks
What is the purpose of spare disks?
Increase aggregate capacity
Replace failed disks
Zeros disk automatically when the disk is
brought into use It is best to zero drives in the spares pool in
advance, allowing Data ONTAP to use the
drives immediately
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Sizing
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Disk Sizing
To properly provision NetApp storage systems,
you must know how disk sizes are calculated:
All disks are right-sized
Count the size of data disks, not parity disks
NOTE: The df command does not reflect parity disks.
Use df -h to view the output in a format you
can read
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Right-Sizing
Disk Type Disk Size Right-Sized Capacity Available Blocks
FC/SCSI 72 GB 68 GB 139,264,000
144 GB 136 GB 278,528,000
300 GB 272 GB 557,056,000
ATA/SATA 160 GB 136 GB 278,258,000
250 GB 212 GB 434,176,000
320 GB 274 GB 561,971,200
500 GB 423 GB 866,531,584
NOTE: ATA drives have only 512 bytes per sector and lose an
additional 1/9 or 12.5% due to block checksum allocation.
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Usable Disk Space
When disks are right-sized, 10% of the space
is reserved for WAFL. This reserved space is:
Used for system and core usage to maximize
disk efficiency
Similar to other operating systems (for example,the UNIX FFS)
The space that remains after right-sizing is
usable disk space, which can be used for
either:
Traditional volumes
Aggregates with flexible volumes
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Disk Space Allocation: Aggregates
Aggregates with a
Traditional VolumeEachaggregate has 10%allocated for WAFL.
Traditional VolumesEachvolume has 20% allocatedfor Snapshot reserve. The
remainder is used for clientdata.
Snapshot ReserveTheamount of space allocatedfor Snapshot reserve is
adjustable. To use thisspace for data (notrecommended), you mustmanually override theallocation used forSnapshot copies.
WAFL Overhead
WAFL Aggregate
Space
10%
90%
Aggregate
Space
80%
20%(Adjustable)
Snapshot Reserve
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Disk Space Allocation: Flexible Volumes
AggregatesEach
aggregate has 5%allocated for Snapshotreserve and 10% allocatedfor WAFL.
Flexible VolumesEachvolume has 20% allocated
for Snapshot reserve. Theremainder is used for clientdata.
Snapshot ReserveTheamount of space allocated
for Snapshot reserve isadjustable. To use thisspace for data (notrecommended), you mustmanually override theallocation used for
Snapshot copies.
FlexVol
Space
Plus
Aggregate
Snapshot
Reserve
WAFL Overhead
WAFL Aggregate
Space
10%
90%
Aggregate
Space
95%
5%(Adjustable)
Aggregate Snapshot Reserve
FlexVol1x
FlexVol#n
.snapshot 20%
80%
20%
80%
.snapshot
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Disk Protection
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Disk Protection
Data ONTAP protects disks through:
RAID
Disk scrubbing
Data ONTAP can assist in recovering from disk
failures
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RAID Groups
RAID groups are a collection of data disks and
parity disks
RAID groups provide protection through parity
Data ONTAP organizes disks into RAID groups
Data ONTAP supports:
RAID 4
RAID-DP
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RAID 4 Technology
RAID 4 protects against data loss that results from a
single-disk failure in a RAID group
A RAID 4 group requires a minimum of two disks:
One parity disk
One data disk
Parity Data Data Data Data Data Data Data
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RAID-DP Technology
RAID-DP protects against data loss that results from
double-disk failures in a RAID group A RAID-DP group requires a minimum of three disks:
One parity disk
One double-parity disk
One data disk
Parity Double-
Parity
Data Data Data Data Data Data
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RAID Group Size
RAID-DP
NetApp
Platform MinimumGroup Size MaximumGroup Size DefaultGroup SizeAll storage systems (with
SATA disks) 3 16 14All storage systems (with
FC disks) 3 28 16
RAID 4
NetApp
Platform MinimumGroup Size MaximumGroup Size DefaultGroup SizeFAS270 2 14 7
All other storage systems
(with SATA) 2 7 7All other storage systems
(with FC) 2 14 8
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Data Reliability
RAID-level checksums enhance data
protection and reliability
Two processes:
options raid.media_scrub
Checks for media errors only If enabled, runs continuously in the background
options raid.scrub(also called disk
scrubbing)
Checks for media errors
Corrects parity consistency
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RAID Checksums
Zone Checksums (ZCS)
Eight 512-byte sectors (4,096 bytes) per block
Every 64th block checksums the previous 63
WAFL never uses these checksum blocks; RAID does
Available for V-Series
Block Checksums (BCS)
Eight 512-byte sectors (4096 bytes) per block
Every sector checksums itself
Are faster than ZCS
Are the standard for FC, SCSI and V-Series disks
8/9ths ATA disks; every ninth sector checksums the
previous eight
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Comparing Media and RAID Scrubs
A media scrub:
Is always running in thebackground when the storagesystem is not busy
Looks for unreadable blocksat the lowest level (0s and 1s)
Is unaware of the data stored
in a block Takes corrective action when
it finds too many unreadableblocks on a disk (sendswarnings or fails a disk,depending on findings)
A RAID scrub:
Is enabled by default Can be scheduled or disabled
Disabling is notrecommended
Uses RAID checksums
Reads a block and then
checks the data If the RAID scrub finds a
discrepancy between theRAID checksum and the dataread, it re-creates the datafrom parity and writes it back
to the block Ensures that data has not
become stale by readingevery block in an aggregate,even when users haventaccessed the data
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About Disk Scrubbing
Automatic RAID scrub:
By default, begins at 1 a.m. on Sundays
Schedule can be changed by an administrator
Duration can be specified by an administrator
Manual RAID scrub overrides automaticsettings
To scrub disks manually:
raid.scrub.enable off
And then:aggr scrub start
To view scrub status:
aggr scrub status aggr_name
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RAID Group Options
NOTE: For a complete list of RAID options, see your product
documentation.
options raid.timeout
options raid.reconstruct.perf_impact
options raid.scrub.enable
options raid.scrub.perf_impact
vol options raidtype
aggr options raidtype
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disk Commands
disk fail diskname
disk remove diskname
disk swap
disk unswap
disk replace [start|stop]
disk zero spares
disk scrub [start|stop]
disk sanitize
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Disk Failures
Spares are global.
Raid Group 0 Spares
Volume 1
DataData DataParity
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Degraded Mode
Degraded mode occurs when:
A single disk fails in a RAID 4 group with no spares Two disks fail in a RAID-DP group with no spares
Degraded modes operates for 24 hours, during whichtime:
Data is still available
Performance is less-than-optimal Data must be recalculated from the parity until the failed disk
is replaced
CPU usage increases to calculate from parity
System shuts down after 24 hours
To change time interval, use the optionsraid.timeout command
If an additional disk in the RAID group fails duringdegraded mode, the result will be data loss
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Replacing a Failed Disk by Hot Swapping
Hot-swapping is the process of removing or
installing a disk drive while system is running
and allows for:
Minimal interruption
The addition of new disks as needed Removing two disks from a RAID 4 group:
Double-disk failure
Data loss will occur
Removing two disks from a RAID-DP group:
Degraded mode
No data loss
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Replacing Failed Disks
NOTE: Disk resizing occurs if a smaller disk is replaced by a
larger one.
1 TB 750 GB 750 GB 750 GB 750 GB
750 GB
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Aggregates
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Aggregates
Aggregates representphysicalstorage:
Made up of one or more RAID groups
A RAID group includes:
One or more data disks
Parity disks
RAID 4 has only one parity disk
RAID-DP has two parity disks
Data is striped for parity protection
A flexible volume depends on an aggregate for
physical storage
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Naming Rules for Aggregates
An aggregate name must:
Begin with either a letter or the underscore
character (_)
Contain only letters, digits, and underscore
characters (_) Contain no more than 255 characters
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Adding an Aggregate
To add an aggregate using the CLI:
aggr create
To add an aggregate using FilerView, use theAggregate Wizard
When adding aggregates, you must have thefollowing information available:
Aggregate name
Parity (DP is default)
RAID group size (minimum) Disk selection method
Disk size
Number of disks (including parity)
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Creating an Aggregate Using the CLI
The following is an example of a CLI entry used
to create an aggregate:
system> aggr create aggr_name 24
Creates an aggregate called aggr_name with24 disks
By default, this aggregate uses RAID-DP
Using the default, 4 of the 24 disks are paritydrives
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Common Aggregate Commands
aggr create [options]
aggr add [options]
aggr status [options]
aggr rename
aggr show_space [-b] aggr offline { | }
aggr online { | }
aggr destroy { | }
Creating an Aggregate Using
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Creating an Aggregate Using
the FilerView Aggregate Wizard
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Aggregate Size
In Data ONTAPprior to version 7.3:
Aggregate size is calculated using:
sysconfig r
All disks in the aggregate (parity and data) are
includedIn Data ONTAP 7.3:
Aggregate size is calculated using the size of
data disks Only data disks in the aggregate are included
(parity disks are excluded)
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Module Summary
In this module, you should have learned to:
NetApp supports FC-AL and SATA disk drives
Use either FilerView or the CLI to find disk
information
Data ONTAP organizes disks into RAID groups
RAID groups consist of data disks and parity
disks
Degraded mode occurs when a single diskfails in a RAID 4 group with no spares, or two
disks fail in a RAID-DP group with no spares
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Exercise
Module 6: Physical Storage
ManagementEstimated Time: 60 minutes
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Answers
Module 6: Physical Storage
Management
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Check Your Understanding
What is a RAID group?
A collection of disks organized to protect data
that includes:
One or more data disks
Data striped for performance One or two parity disks for protection
Why use double parity?
To protect against a double-disk failure
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Check Your Understanding (Cont.)
How many RAID groups does the following
command create?aggr create newaggr 32
Assuming a default RAID group size of 16, this
creates two RAID groups What is the minimum size of a RAID-DP
group?
Three disks (one data, two parity)