Re: Issue with fstrim and Nova hw_disk_discard=unmap

Fulvio Galeazzi <fulvio.galeazzi@xxxxxxx> · Wed, 14 Mar 2018 08:29:36 +0100

Hallo Jason, sure here it is!

rbd --cluster cephpa1 -p cinder-ceph info 
volume-80838a69-e544-47eb-b981-a4786be89736
rbd image 'volume-80838a69-e544-47eb-b981-a4786be89736':
        size 15360 MB in 3840 objects
        order 22 (4096 kB objects)
        block_name_prefix: rbd_data.9e7ffe238e1f29
        format: 2
        features: layering, exclusive-lock, object-map, fast-diff, 
deep-flatten
        flags:

  Thanks

		Fulvio

-------- Original Message --------
Subject: Re:  Issue with fstrim and Nova hw_disk_discard=unmap
From: Jason Dillaman <jdillama@xxxxxxxxxx>
To: Fulvio Galeazzi <fulvio.galeazzi@xxxxxxx>
CC: Ceph Users <ceph-users@xxxxxxxxxxxxxx>
Date: 03/13/2018 06:33 PM

Can you provide the output from "rbd info <pool
name>/volume-80838a69-e544-47eb-b981-a4786be89736"?

On Tue, Mar 13, 2018 at 12:30 PM, Fulvio Galeazzi
<fulvio.galeazzi@xxxxxxx> wrote:
Hallo!

Discards appear like they are being sent to the device.  How big of a
temporary file did you create and then delete? Did you sync the file
to disk before deleting it? What version of qemu-kvm are you running?

I made several test with commands like (issuing sync after each operation):

dd if=/dev/zero of=/tmp/fileTest bs=1M count=200 oflag=direct

What I see is that if I repeat the command with count<=200 the size does not
increase.

Let's try now with count>200:

NAME                                        PROVISIONED  USED
volume-80838a69-e544-47eb-b981-a4786be89736      15360M 2284M

dd if=/dev/zero of=/tmp/fileTest bs=1M count=750 oflag=direct
dd if=/dev/zero of=/tmp/fileTest2 bs=1M count=750 oflag=direct
sync

NAME                                        PROVISIONED  USED
volume-80838a69-e544-47eb-b981-a4786be89736      15360M 2528M

rm /tmp/fileTest*
sync
sudo fstrim -v /
/: 14.1 GiB (15145271296 bytes) trimmed

NAME                                        PROVISIONED  USED
volume-80838a69-e544-47eb-b981-a4786be89736      15360M 2528M

As for qemu-kvm, the guest OS is CentOS7, with:

[centos@testcentos-deco3 tmp]$ rpm -qa | grep qemu
qemu-guest-agent-2.8.0-2.el7.x86_64

while the host is Ubuntu 16 with:

root@pa1-r2-s10:/home/ubuntu# dpkg -l | grep qemu
ii  qemu-block-extra:amd64               1:2.8+dfsg-3ubuntu2.9~cloud1
amd64        extra block backend modules for qemu-system and qemu-utils
ii  qemu-kvm                             1:2.8+dfsg-3ubuntu2.9~cloud1
amd64        QEMU Full virtualization
ii  qemu-system-common                   1:2.8+dfsg-3ubuntu2.9~cloud1
amd64        QEMU full system emulation binaries (common files)
ii  qemu-system-x86                      1:2.8+dfsg-3ubuntu2.9~cloud1
amd64        QEMU full system emulation binaries (x86)
ii  qemu-utils                           1:2.8+dfsg-3ubuntu2.9~cloud1
amd64        QEMU utilities

   Thanks!

                         Fulvio

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