2011-09-14 07:55 AM
Looking for direction on adding 2 new DS4243 shelves into our existing FAS2040 environment. Focusing on properly distributing the addition of the 48 new disks.
Internal disks are 12x450GB SAS
2 DS4243 Shelves, 24x450GB SAS and 24x1TB SATA
Aggr0 - RAID Size 24 - SAS, Total 2.87TB, 10 disks
Aggr1 - RAID Size 14 - SATA, Total 7.27TB, 12 disks
Aggr0 - RAID Size 28 - SAS, Total 8.61TB, 26 disks
Aggr1 - RAID Size 14 - SATA, Total 6.22TB, 11 disks
1 spare SATA
I'm not fully understanding the RAID size aspect of the aggregates, but I do know the aggregate maximum size is 16TB (Is that RAW size or not?)
If I understand things I've read, the larger the RAID size to better the performance is because the data is striped across more disks but if a disk fails then rebuilding will take much longer.
Is there any kind of charts for layout of disks based on the disk size?
2011-09-14 01:45 PM
16TB limit is not raw, it is usable, so e.g. the maximum spindle count for 1TB drives is 23 for ONTAP 7.3.4.
Bigger RAID groups are not necessarily better for performance (an aggregate can span multiple RGs, so can a volume), but there is less capacity overhead (fewer parity drives).
I am suggesting reading up this doc:
Storage Subsystem Technical FAQ
2011-09-15 08:19 AM
Thank you for all the documentation to read, TR and community posts. I will soak them in during the next couple of days. A quick question though, can the RAID group size be changed on an aggregate without data lost? If so, what is the proper way of doing so and what are the negatives of making such change. Thanks.
2011-09-15 08:45 AM
While you cannot subtract from a raidgroup you can modify the maximum size and add. It will warn you if certain raidsizes are not supported in earlier ontap releases.
This gives the current raidsize setting:
vol options <volname>
This modifies the raidsize:
vol options <volname> raidsize <setting>
I'd imagine its much easier using your gui of choice.
In general I prefer to decide on what my ideal raidsize is when I initially create the aggregate. Diverging from this setting shouldn't have any affect if one rg is 1-2 disks larger than the other and you are topping out its maximum size.
I usually think about it as trade off between rebuild times and performance or max usable capacity.
Have a look at this for a more in depth discussion: