What is the max raid group size for 1 TB SATA disks

[bharatjasti]

Hi All,

Can any one tell me i wan to create raid 4 aggr with 14*1 TB SATA disks, what is the max. raid group size i can create for raid4 aggr for 1TB SATA drives.

[aborzenkov]

RAID4 SATA group has size limit of 8 disks. You are definitely better off using RAID_DP (16 disks max).

[bharatjasti]

But i read somewhere max rg size is 12, can't i use more than 8 ..?

[scottgelb]

use the -r option to specify raid size for an aggregate in the aggr create command.  I would not run RAID4 with SATA (always DP), but the default raid group size is 8 and the max is 14 with single parity.  As of 8.0.1 with dual parity, the max raid group size is 20.  I would rather see an 18D+2P raid group than a 13D+1P raid group so that you get dual parity protection.

[aborzenkov]

the default raid group size is 8 and the max is 14 with single parity

Nope, we are both wrong. For SATA max raid4 group size is 7. This limit did not change in 8.x. You are right that for RAID_DP limit was raised to 20, although this probably does not matter for 14 disks anyway

[scottgelb]

I have go be wrong once a day, so may as well make it early    I have to update my notes for single parity (somewhere had the change written in the disk setup) but haven't used single parity in years....never could responsibly setup 1 or 2TB drives without dual parity... we do have more customers going with larger SATA raid_dp raid groups now with 8.0 and is nice be able to go over 14 now.

[scottgelb]

Yep...just checked Jay White's updated Storage Subsystem FAQ and updated to show single parity SATA is default and max of 7 drive raid groups... no reason to every go single parity with the same overhead for DP with 14 drives.

[aborzenkov]

You can create aggregate consisting of several raid groups (up to the max aggregate size limit), but as already mentioned it is far better to use RAID_DP; in which case you can have single raid group with 12 disks.