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Considerations for sizing RAID groups for drives
Configuring an optimum RAID group size for an aggregate made up of drives requires a trade-off of factors. You must decide which factor—speed of recovery, assurance against data loss, or maximizing data storage space—is most important for the aggregate that you are configuring.
You change the size of RAID groups on a per-aggregate basis. You cannot change the size of an individual RAID group.
HDD RAID groups
You should follow these guidelines when sizing your RAID groups composed of HDDs:
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All RAID groups in an aggregate should have the same number of disks.
If this is impossible, any RAID group with fewer disks should have only one less disk than the largest RAID group.
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The recommended range of RAID group size is between 12 and 20.
The reliability of performance disks can support a RAID group size of up to 28, if needed.
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If you can satisfy the first two guidelines with multiple RAID group sizes, you should choose the larger size.
SSD RAID groups in Flash Pool aggregates
The SSD RAID group size can be different from the RAID group size for the HDD RAID groups in a Flash Pool aggregate. Usually, you should ensure that you have only one SSD RAID group for a Flash Pool aggregate, to minimize the number of SSDs required for parity.
SSD RAID groups in SSD-only aggregates
You should follow these guidelines when sizing your RAID groups composed of SSDs:
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All RAID groups in an aggregate should have the same number of drives.
If this is impossible, any RAID group with fewer drives should have only one less drive than the largest RAID group.
•
The recommended range of RAID group size is between 20 and 28.

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