degraded RAID performance after OS upgrade, and drives added.
cswiger at mac.com
Thu Nov 30 12:01:55 PST 2006
On Nov 30, 2006, at 11:40 AM, Derrick MacPherson wrote:
> That seems like a pretty crazy drop in performance, more than one
> would expect. The machine is busy but not busy enough to warrant
> this.. Imo.. Is there a way to test to confirm?
Using dd is a trivial benchmark, and not especially precise but good
enough to give rough answers; otherwise, there are lots of I/O
benchmarks in ports like iozone or even "diskinfo -t". Try using
different block sizes while reading and writing with dd, and you'll
probably find some useful info.
While it is likely that you can adjust the RAID-5 stripe size, change
the write-caching from write-thru to write-back (if your RAID has a
battery, anyway, otherwise this is dangerous), etc, using a 3-disk
RAID-5 volume is just not a great idea-- RAID-5 is happier with more
drives than the minimum of 3 to get better parallelism and reduce the
overhead for parity info.
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