On 10/12/14 21:30, Strahinja Kustudić wrote:
> On Wed, Dec 10, 2014 at 4:55 AM, Mark Kirkwood <
> mark.kirkwood@catalyst.net.nz> 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
