JasonCzerak wrote:
Or is there some sort of performance penalty going up to 28 disks because of how the algorithms work?
The resiliency guide is silent on issues of performance. Pg. 22 says
Smaller RAID groups
Use smaller RAID groups for faster reconstructions and reduced risks during reconstruction.
Page 11:
NetApp recommends using the default RAID group sizes when using RAID-DP.
Page 4:
Use the default RAID group size when creating aggregates or traditional volumes.
All disks in an aggregate are supposed to participate in IO operations. There is a performance penalty during reconstruction as well as risks; "smaller" RG sizes are meant to minimize both.
There is a maximum number of data disks that can contribute space to an aggregate for a 16TB aggregate composed entirely of a give disk size, so I've seen RG sizes deviate from the recommended based on that factor (You don't want/need a RG of 2 data+2parity just to add 2 more data disks to an aggr....). Minimizing losses to parity is not a great solution to any capacity issue.
my $0.02.
Message was edited by: evilensky