Re: Very low 4k randread performance ~1000iops

Stephen Mercier <stephen.mercier@xxxxxxxxxxxx> · Tue, 30 Jun 2015 10:32:27 -0700

I ran into the same problem. What we did, and have been using since, is increased the read ahead buffer in the VMs to 16MB (The sweet spot we settled on after testing). This isn't a solution for all scenarios, but for our uses, it was enough to get performance inline with expectations.
In Ubuntu, we added the following udev config to facilitate this:

root@ubuntu:/lib/udev/rules.d# vi /etc/udev/rules.d/99-virtio.rules 

SUBSYSTEM=="block", ATTR{queue/rotational}=="1", ACTION="" KERNEL=="vd[a-z]", ATTR{bdi/read_ahead_kb}="16384", ATTR{queue/read_ahead_kb}="16384", ATTR{queue/scheduler}="deadline"

Cheers,

-- 
Stephen Mercier
Senior Systems Architect
Attainia, Inc.
Phone: 866-288-2464 ext. 727
Email: stephen.mercier@xxxxxxxxxxxx
Web: www.attainia.com

Capital equipment lifecycle planning & budgeting solutions for healthcare

On Jun 30, 2015, at 10:18 AM, Tuomas Juntunen wrote:

Hi

It’s not probably hitting the disks, but that really doesn’t matter. The point is we have very responsive VM’s while writing and that is what the users will see.
The iops we get with sequential read is good, but the random read is way too low.

Is using SSD’s as OSD’s the only way to get it up? or is there some tunable which would enhance it? I would assume Linux caches reads in memory and serves them from there, but atleast now we don’t see it.

Br,
Tuomas

From: Somnath Roy [mailto:Somnath.Roy@xxxxxxxxxxx] 
Sent: 30. kesäkuuta 2015 19:24
To: Tuomas Juntunen; 'ceph-users'
Subject: RE:  Very low 4k randread performance ~1000iops

Break it down, try fio-rbd to see what is the performance you getting..
But, I am really surprised you are getting > 100k iops for write, did you check it is hitting the disks ?

Thanks & Regards
Somnath

From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Tuomas Juntunen
Sent: Tuesday, June 30, 2015 8:33 AM
To: 'ceph-users'
Subject:  Very low 4k randread performance ~1000iops

Hi

I have been trying to figure out why our 4k random reads in VM’s are so bad. I am using fio to test this.

Write : 170k iops
Random write : 109k iops
Read : 64k iops
Random read : 1k iops

Our setup is:
3 nodes with 36 OSDs, 18 SSD’s one SSD for two OSD’s, each node has 64gb mem & 2x6core cpu’s
4 monitors running on other servers
40gbit infiniband with IPoIB
Openstack : Qemu-kvm for virtuals

Any help would be appreciated

Thank you in advance.

Br,
Tuomas

PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies).
_______________________________________________
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