[ceph-users] Poor libRBD write performance

Moreno, Orlando orlando.moreno at intel.com
Mon Nov 20 09:00:04 PST 2017


Hi Jason,

You're right, thanks for pointing that out. I could've sworn I saw the same problem with exclusive-lock disabled, but after trying it again, disabling the feature does fix the write performance :)

So does this mean that when an RBD is attached to a VM, it is considered a single client connection?

Thanks,
Orlando

-----Original Message-----
From: Jason Dillaman [mailto:jdillama at redhat.com] 
Sent: Monday, November 20, 2017 9:10 AM
To: Moreno, Orlando <orlando.moreno at intel.com>
Cc: fio at vger.kernel.org; ceph-users at lists.ceph.com; cbt at lists.ceph.com
Subject: Re: [ceph-users] Poor libRBD write performance

I suspect you are seeing this issue [1]. TL;DR: never use "numjobs" >
1 against an RBD image that has the exclusive-lock feature enabled.

[1] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2016-August/012123.html

On Mon, Nov 20, 2017 at 11:06 AM, Moreno, Orlando <orlando.moreno at intel.com> wrote:
> Hi all,
>
>
>
> I’ve been experiencing weird performance behavior when using FIO RBD 
> engine directly to an RBD volume with numjobs > 1. For a 4KB random 
> write test at
> 32 QD and 1 numjob, I can get about 40K IOPS, but when I increase the 
> numjobs to 4, it plummets to 2800 IOPS. I tried running the same exact 
> test on a VM using FIO libaio targeting a block device (volume) 
> attached through QEMU/RBD and I get ~35K-40K IOPS in both situations. 
> In all cases, CPU was not fully utilized and there were no signs of 
> any hardware bottlenecks. I did not disable any RBD features and most 
> of the Ceph parameters are default (besides auth, debug, pool size, etc).
>
>
>
> My Ceph cluster is running on 6 nodes, all-NVMe, 22-core, 376GB mem, 
> Luminous 12.2.1, Ubuntu 16.04, and clients running FIO job/VM on 
> similar HW/SW spec. The VM has 16 vCPU, 64GB mem, and the root disk is 
> locally stored while the persistent disk comes from an RBD volume 
> serviced by the Ceph cluster.
>
>
>
> If anyone has seen this issue or have any suggestions please let me know.
>
>
>
> Thanks,
>
> Orlando
>
>
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>



--
Jason


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