"Mike" == Mike Smith mikesmit@netapp.com writes:
Mike> If you want 28 disks in your first raid group. I agree with Mike> Aaron's comment about reconstruct speed. Also the larger the Mike> number of disks in a single raid group the higher the odds Mike> of data loss due to duble disk failure. Please be aware that Mike> if you have too few disks in a raid group you could also Mike> negatively affect the performance. Check this white paper on Mike> www.netapp.com
Mike> http://www.netapp.com/tech_library/3008.html
Mike> According to the "Table 4" in this technical paper 14 disks Mike> per raid group provides optimal performance. --
Keep in mind a few things. That paper measures performance on older filers (F330's and earlier) using SCSI disks and reduced RAM (256 and less) sizes. While the principles are obviously sound, you should want to do some testing in your own environment.
You should also balance any performance gains against the increased risk of losing data by using larger RAID group sizes. Unless I needed every last ounce of performance or data capacity, I'd lean toward the smaller RAID group sizes. See:
http://www.netapp.com/tech_library/3027.html
for a discussion of how to compute Mean Time to Data Loss with different size RAID groups.
For our application, we chose to use a RAID group size of 6.
I've seen our F740's push 10K ops/sec with acceptable response times in a heavy-read/random-access intense (web serving) environment. Cache age is < 1, so we could definitly benefit by bumping our F740's to 1GB cache from 512MB. That's with the size 6 RAID group.
j. -- Jay Soffian jay@cimedia.com UNIX Systems Engineer 404.572.1941 Cox Interactive Media