Recommended RAID group size in an aggregate spanning 2 DS2246 shelves & 1.2TB 10K SAS disks please?

[rh]

Hi We have just added two DS2246 shelves containing 1.2TB 10K SAS disks to a FAS3240 filer. Since the new disks are unique to the new shelves (ie no existing spares of that type), I came up with the following two choices for RAID group size: (A) 3 x 15 and three spares (B) 2 x 23 and two spares What are the pros and cons, please, of these choices or can you think of a better layout, perhaps? Regards, Richard.

[cgeck0000 · Accepted solution]

You want option B.

Option (A) has the cons:

 - You lose 2 additional disks to parity using 3 RAID groups

 - You lose an additional disk as a hot spare

 - When you add an additional shelf you will have 12 spare disks to decide what to do with

 - Bottom line you have less space with this option

Option (B)

 - No cons I can think of

 - Pro -> More space than option (A)

 - Pro -> More data disks in the aggregate thus giving you slightly more IOPS

 - Easily add another shelf and use 23 disks with 3 hot spares

[paulstringfellow]

i think i'd be looking option B as well... the only thing i'd look for is when you create new aggregates and a new raid group, make sure you manualy select the disks to go in the RG, otherwise you will potentially end up with the disk in the preveious shelf been in the new RAID group, alhtough technically this isn't a problem, if you are thinking about logical boundaries to manage your raw disks, then it's a consideration.

[rh]

Many thanks to CGECK0000 and Paul Stringfellow for their very helpful responses. Regards, Richard.