Hello Wido,
I have looked at the libvirt code and there is a check to ensure that fast-diff is enabled on the image and only then does it try to get the real disk usage. The issue for me is that even with fast-diff enabled it takes 25min to get the space usage for a 50TB image.
I had considered turning off fast-diff on the large images to get around to issue but I think that will hurt my snapshot removal times ( untested )
I can't see in the code any other way of bypassing the disk usage check but I am not that familiar with the code.
-------------------
if (volStorageBackendRBDUseFastDiff(features)) {
VIR_DEBUG("RBD image %s/%s has fast-diff feature enabled. "
"Querying for actual allocation",
def->source.name, vol->name);
if (virStorageBackendRBDSetAllocation(vol, image, &info) < 0)
goto cleanup;
} else {
vol->target.allocation = info.obj_size * info.num_objs;
}
------------------------------
Kind regards,
Glen Baars
-----Original Message-----
From: Wido den Hollander <wido@xxxxxxxx>
Sent: Thursday, 28 February 2019 3:49 PM
To: Glen Baars <glen@xxxxxxxxxxxxxxxxxxxxxx>; ceph-users@xxxxxxxxxxxxxx
Subject: Re: Mimic 13.2.4 rbd du slowness
On 2/28/19 2:59 AM, Glen Baars wrote:
> Hello Ceph Users,
>
> Has anyone found a way to improve the speed of the rbd du command on large rbd images? I have object map and fast diff enabled - no invalid flags on the image or it's snapshots.
>
> We recently upgraded our Ubuntu 16.04 KVM servers for Cloudstack to Ubuntu 18.04. The upgrades libvirt to version 4. When libvirt 4 adds an rbd pool it discovers all images in the pool and tries to get their disk usage. We are seeing a 50TB image take 25min. The pool has over 300TB of images in it and takes hours for libvirt to start.
>
This is actually a pretty bad thing imho. As a lot of images people will be using do not have fast-diff enabled (images from the past) and that will kill their performance.
Isn't there a way to turn this off in libvirt?
Wido
> We can replicate the issue without libvirt by just running a rbd du on the large images. The limiting factor is the cpu on the rbd du command, it uses 100% of a single core.
>
> Our cluster is completely bluestore/mimic 13.2.4. 168 OSDs, 12 Ubuntu 16.04 hosts.
>
> Kind regards,
> Glen Baars
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