How Data ONTAP uses RAID

How Data ONTAP uses RAID

RAID-DP

uses two parity disks to ensure data recoverability even if two
disks within the RAID group fail

RAID4

Uses one parity disk to ensure data recoverability if one disk fails within the RAID
group.

Data disk

Holds data stored on behalf of clients within RAID groups (and
any data generated about the state of the filer as a result of a
malfunction).

Hot spare disk

Does not hold usable data, but is available to be added to a RAID
group in an aggregate. Any functioning disk that is not assigned
to an aggregate functions as a hot spare disk.

Parity disk

Stores data reconstruction information within RAID groups.

dParity disk

Stores double-parity information within RAID groups, if RAIDDP
is enabled


Replace Disk:

Disk replace start [-f] old_disk new_spare
-f suppresses confirmation information being displayed


Maximum number of RAID groups

Data ONTAP supports up to 400 RAID groups per filer or cluster



What a plex

A plex is a collection of one or more RAID groups that together provide the
storage for one or more WAFL® (Write Anywhere File Layout) file system
volumes. Data ONTAP uses plexes as the unit of RAID-level mirroring when the
SyncMirror® feature is enabled

What an aggregate

An aggregate is a collection of one or two plexes, depending on whether you
want to take advantage of RAID-level mirroring

When you create an aggregate, Data ONTAP assigns data disks and parity disks
to RAID groups, depending on the options you choose, such as the size of the
RAID group

aggregates to manage plexes and RAID groups because these entities
only exist as part of an aggregate

You can increase the usable space in an
aggregate by adding disks to existing RAID groups or by adding new RAID
groups.

Once you’ve added disks to an aggregate, you cannot remove them to
reduce storage space without first destroying the aggregate

SyncMirror feature is licensed and enabled, you can convert an unmirrored
aggregate to a mirrored aggregate and vice versa without any downtime

Maximum Number of aggregate we can create up to 100.
aggr status –s

-s displays a listing of the spare disks on the filer.

For size in kilobytes, enter:

df -A aggr0
For size in 4096-

aggr status { -d | -r } aggr0
-d displays disk information
-r displays RAID information


Creating aggregare:

aggr create [ -m ] [-r raidsize] aggr ndisks[@disksize]
Example:

aggr create aggr1 24@72G

Result: An aggregate named aggr1 is created. It consists of 24 72-
GB disks.
-m instructs Data ONTAP to implement SyncMirror.
-r raidsize specifies the maximum number of disks of each RAID
group in the aggregate. The maximum and default values for raidsize
are platform-dependent, based on performance and reliability
considerations


By default, the RAID level is set to RAID-DP. If raidsize is sixteen,
aggr1 consists of two RAID groups, the first group having fourteen
data disks, one parity disk, and one double parity disk, and the
second group having six data disks, one parity disk, and one double
parity disk

Verify AGGR Status:

aggr status aggr1

Aggregate Copy:

aggr copy start src_aggr dest_aggr

Copies the specified aggregate and its FlexVol volumes to a different
aggregate on a new set of disks.