Eduardo Bragatto wrote:
On Mar 1, 2010, at 4:04 PM, Tim Cook wrote:
The primary concern as I understand it is performance. If they're
close in size, it shouldn't be a big deal, but when you've got
mismatched rg's it can cause quite the performance troubleshooting
nightmare. It's the same reason you don't want to make a pool that
has one raid group that's entirely 15kRPM SAS drives and the other
5400RPM SATA.
Thanks, Tim. I just finished some tests and they ratify exactly what
you said.
If it's of anyone else's interest, here's a brief description of my
experiment.
I have setup three different pools using a total of 15 disks:
Case #1 - 3 x raidz ( 5 + 5 + 5 disks )
Case #2 - 2 x raidz ( 7 + 7 disks) + 1 spare
Case #3 - 2 x raidz ( 7 + 8 disks)
As expected, performance was higher in case #1 and worst in case #3.
The differences, however, happened only to write operations with files
larger than 1GB.
You would also see a performance hit when the pool is getting full, the
smaller vdev will fill and all the I/O will be on the bigger one.
--
Ian.
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