On 10/12/14 21:30, Strahinja Kustudić wrote:
On Wed, Dec 10, 2014 at 4:55 AM, Mark Kirkwood <
mark.kirkwood@xxxxxxxxxxxxxxx> wrote:
That is interesting: I've done some testing on this type of card with 16
(slightly faster Hitachi) SSD attached. Setting WT and NORA should enable
the so-called 'fastpath' mode for the card [1]. We saw performance improve
markedly (300MB/s random write go to 1300MB/s).
This *might* be related to the fact that 16 SSD can put out more IOPS than
the card can actually handle - whereas your 8 S3500 is probably the perfect
number (e.g 8*11000 = 88000 which the card can handle ok).
[1] If you make the change while there are no outstanding background
operations (array rebuild etc) in progress (see
http://www.flagshiptech.com/eBay/Dell/poweredgeh310h710h810UsersGuide.pdf
).
I read that guide too, which is the reason why I tried with WT/NORA, but
the document also states: "NOTE: RAID 10, RAID 50, and RAID 60 virtual
disks cannot use FastPath." Which is a little odd, since usually if you
want performance with reliability, you go RAID10.
Do you have any suggestions what I could try to tweak to get more
performance?
We are using these configured as *individual* drives on RAID0 that are
then md raided in a (software) RAID 10 array. Maybe try that out (as
fastpath only cares about the HW RAID setup).
Interestingly we were also seeing better performance on a fully HW RAID
10 array with WT/NORA...so (I guess) our Hitachi SSD probably have lower
latency than the S3500 does.
Cheers
Mark
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