Steve Bergman wrote:
I've used both CFQ and Deadline for testing. It doesn't make a
measurable difference for either the multiple dd's or for the
single-threaded C/ISAM rebuild. (In fact, deadline, while often better
for servers, can have problems with mixed sequential/random access
workloads. At least according to what I've seen over on the PostgreSQL
lists. It's no surprise that deadline doesn't help my single-threaded
workload. Also note that deadline has shown itself to be slightly
superior to noop for SSD's in certain benchmarks.) There's no one size
fits all answer. Until the particular workload is actually tested, it
*is* guesswork. I/O scheuling is too complicated for it to be
otherwise.
Can't say one way or the other on SSD, but I can't measure any big benefit of
deadline on RAID-5 or RAID-10. I haven't done proper testing on RAID-6, so I
can't say.
Since this is an unusual RAID10 situation, and I have plenty of spare
processor available, I'm going to try RAID5 over the weekend. I've
never used it. But I'm guessing that parity might come at a lower
bandwidth cost than mirroring. Should be a fun weekend. :-)
When testing RAID-10, but sure you set it up for 'far' copies, since this should
improve transfer rate, particularly under single thread read.
--
Bill Davidsen <davidsen@xxxxxxx>
We are not out of the woods yet, but we know the direction and have
taken the first step. The steps are many, but finite in number, and if
we persevere we will reach our destination. -me, 2010
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