On Mon, Mar 13, 2017 at 6:09 AM, Florian Haas <florian@xxxxxxxxxxx> wrote:
> On Mon, Mar 13, 2017 at 11:00 AM, Dan van der Ster <dan@xxxxxxxxxxxxxx> wrote:
>>> I'm sorry, I may have worded that in a manner that's easy to
>>> misunderstand. I generally *never* suggest that people use CFQ on
>>> reasonably decent I/O hardware, and thus have never come across any
>>> need to set this specific ceph.conf parameter.
>>
>> OTOH, cfq *does* help our hammer clusters. deadline's default
>> behaviour is to delay writes up to 5 seconds if the disk is busy
>> reading -- which it is, of couse, while deep scrubbing. And deadline
>> does not offer any sort of fairness between processes accessing the
>> same disk (which is admittedly less of an issue in jewel). But back in
>> hammer days it was nice to be able to make the disk threads only read
>> while the disk was otherwise idle.
>
> Thanks for pointing out the default 5000-ms write deadline. We
> frequently tune that down to 1500ms. Disabling front merges also
> sometimes seems to help.
>
> For the archives: those settings are in
> /sys/block/*/queue/iosched/{write_expire,front_merges} and can be
> persisted on Debian/Ubuntu with sysfsutils.
Hey Florian :).
I wrote a quick udev rule to do this on Ubuntu, here is is for others'
reference. Also saw earlier a recommendation to increase
read_ahead_kb to 4096 for slower spinning disks
root@croc1:/etc/udev/rules.d# cat 99-storcium-hdd.rules
# Set write deadline to 1500 and disable front merges, and increase
read_ahead_kb to 4096
ACTION=="add|change", KERNEL=="sd*", SUBSYSTEM=="block",
ATTR{queue/iosched/write_expire}="1500",
ATTR{queue/iosched/front_merges}="0", ATTR{queue/read_ahead_kb}="4096"
Best regards,
Alex
>
> Cheers,
> Florian
> _______________________________________________
> ceph-users mailing list
> ceph-users@xxxxxxxxxxxxxx
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
