RAID Group Size with disk expansion

[DAVID_FRUITERMAN]

I have a FAS3210A with each head owning a DS4243 shelf of 1 TB SATA drives.  Current RAID group size is 16.  There are only 18 disk populated in each shelf (6 empty bays).  2 disks are hot spares for each shelf.  Here's my question.  I have 6 disks to add to each shelf, which will max out the shelf with 24 drives.  Do I expand the RAID group size or keep it the same.  If I keep it at 16, then I'm only going to get to use 4 out of the 6 drives, b/c it will create new parity drives.  If I expand the RAID group size, will this affect performance?  How badly will performance be affected?  Also, what is the maximum RAID group size for a 3210 with 1 TB SATA drives.  We're currently running ONTAP 7.3.5P1 on this cluster, with the idea of upgrading to 8.1.3P2 in the near future.

Thanks in advance for any info!

[KHAN_FAISAL]

Hi David,

The maximum RAID group size is 28, yes you can very well expand the current RAID group but you will have to face a little performance challenge. however the performance is not a big concern if you are expanding to 28 RAID group size, the major concern is the resiliency because after expanding it to 28 RAID group size you have more data disk to protect in a less parity drive. 

[aborzenkov]

The maximum RAID group size is 28

Max RG size for SATA disks is 16 in 7.3 and 20 in 8.1.

[KHAN_FAISAL]

I apologize i though of SAS drives because there the maximum RAID group size is 28. anyways as per your current config i guess you have created 15D+2P+1S. if that is the case then you can add another 6 disk and expand it to 20D+2P+2S.

[DAVID_FRUITERMAN]

20D + 2P + 2S would be a 22 Raid group size.  If the max is 20 for SATA on 7.3 then that wouldn't work.

[KHAN_FAISAL]

Yes, david i have just checked in my simulator and it is not possible to go ahead with that config. now i guess you dont have any choice. either you can create new RAID group or you can expand it to 18D+4P+2S with the minimal performance overhead.