Re: How to estimate whether putting a journal on SSD will help with performance?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi,

On 01.05.2015 10:30, Piotr Wachowicz wrote:
> Is there any way to confirm (beforehand) that using SSDs for journals
> will help?
yes SSD-Journal helps a lot (if you use the right SSDs) for write speed,
and I made the experiences that this also helped (but not too much) for
read-performance.

>
> We're seeing very disappointing Ceph performance. We have 10GigE
> interconnect (as a shared public/internal network).
Which kind of CPU do you use for the OSD-hosts?

>
> We're wondering whether it makes sense to buy SSDs and put journals on
> them. But we're looking for a way to verify that this will actually
> help BEFORE we splash cash on SSDs.
I can recommend the Intel DC S3700 SSD for journaling! In the beginning
I started with different much cheaper models, but this was the wrong
decision.
>
> The problem is that the way we have things configured now, with
> journals on spinning HDDs (shared with OSDs as the backend storage),
> apart from slow read/write performance to Ceph I already mention,
> we're also seeing fairly low disk utilization on OSDs. 
>
> This low disk utilization suggests that journals are not really used
> to their max, which begs for the questions whether buying SSDs for
> journals will help.
>
> This kind of suggests that the bottleneck is NOT the disk. But,m yeah,
> we cannot really confirm that.
>
> Our typical data access use case is a lot of small random read/writes.
> We're doing a lot of rsyncing (entire regular linux filesystems) from
> one VM to another.
>
> We're using Ceph for OpenStack storage (kvm). Enabling RBD cache
> didn't really help all that much.
The read speed can be optimized with an bigger read ahead cache inside
the VM, like:
echo 4096 > /sys/block/vda/queue/read_ahead_kb

Udo
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com




[Index of Archives]     [Information on CEPH]     [Linux Filesystem Development]     [Ceph Development]     [Ceph Large]     [Ceph Dev]     [Linux USB Development]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [xfs]


  Powered by Linux