Specifies the maximum number of disks that can exist per RAID group.
The following table lists the supported minimum and maximum RAID-DP group sizes:
|
Platform |
Minimum Group Size |
Maximum Group Size |
|
R200 |
3 |
16 |
|
R150 |
3 |
16 |
|
R100 |
3 |
12 |
|
All other supported platforms |
3 |
28 |
The following table lists the supported minimum and maximum RAID-4 group sizes:
|
Platform |
Minimum Group Size |
Maximum Group Size |
|
R200 |
2 |
7 |
|
R150 |
2 |
6 |
|
R100 |
2 |
8 |
|
FAS250 |
2 |
14 |
|
All other supported platforms |
2 |
14 |
Note: If, as a result of a software upgrade from an older version of Data ONTAP, traditional volumes exist that contain RAID-4 groups larger than the maximum group size for the platform, it is recommended that you convert the traditional volumes in question to RAID-DP as soon as possible.
Advantages of using large RAID groups include the following:
More data drives are available when you use large RAID groups, because fewer drives are used as parity disks.
Read/write operations are usually faster.
Advantages of using small RAID groups include:
Shorter data reconstruction time in case of disk failure.
Decreased risk of data loss due to multiple disk failures. The probability of data loss through double disk failure within a RAID 4 group or through triple disk failure within a RAID DP group is lower within a small RAID group than in a large RAID group.
A RAID-4 group consists of a set of at least one data disk and one parity disk. A RAID-DP group consists of a set of at least one data disk, one regular parity disk, and one double-parity (or dParity) disk.
Data disks contain data from clients. Parity and dParity disks contain information that Data ONTAP uses to reconstruct a failed disk's data in conjunction with other data disks.
If an aggregate is configured for RAID-4 protection, Data ONTAP assigns the role of parity disk to the largest disk in the RAID group. If an aggregate is configured for RAID-DP protection, Data ONTAP assigns the role of dParity disk and regular parity disk to the largest and second-largest disk in the RAID group.
Each aggregate or traditional volume requires at least one RAID group. You cannot assign a RAID group to more than one aggregate or traditional volume.
Data ONTAP supports up to 400 RAID groups per filer or cluster.
Data ONTAP automatically assigns hot spare disks to RAID groups. A hot spare disk is a disk in a disk shelf that does not hold data and is ready for use.
Data ONTAP creates new RAID groups as each RAID group is filled with its maximum number of disks. Hot spare disks do not have to be in the same disk shelf as other disks of a RAID group to be available to that RAID group.
See the Data ONTAP Storage Management Guide for more information about RAID protection.