9:29 a.m.
virt-sparsify: error: libguestfs error: discard cannot be enabled on this
drive: qemu does not support discard for '*parallels*' format files
Since Virtuozzo 7.0.11 discard is officially supported for ploop images
and I've mounted them with discard and confirmed this functionality
works as expected. Would it be possible to update libguestfs to be
aware of this support so the --inplace flag will work?
https://virtuozzosupport.force.com/s/article/VZA-2019-059
"Native discard support in ploop enabling automatic discard requests on
all ext4 filesystems over ploop block devices, except containers running
on Virtuozzo Storage."
--
Jonathan Wright
KnownHost, LLC
https://www.knownhost.com
5 a.m.
Hi Jonathan,
On Thursday, 26 September 2019 16:29:46 CEST Jonathan Wright wrote:
virt-sparsify: error: libguestfs error: discard cannot be enabled on
this
drive: qemu does not support discard for '*parallels*' format files
Correct, this is because we have the following function to determine
whether it is supported:
https://github.com/libguestfs/libguestfs/blob/02890096d55eaee66c1e6ed34fc...
In a nutshell:
- raw supported with qemu >= 1.5
- qcow2 supported with qemu >= 1.6
- any other format is not supported
So we check based on the version of qemu currently.
Since Virtuozzo 7.0.11 discard is officially supported for ploop
images
and I've mounted them with discard and confirmed this functionality
works as expected. Would it be possible to update libguestfs to be
aware of this support so the --inplace flag will work?
https://virtuozzosupport.force.com/s/article/VZA-2019-059
This leads me to the question: how can libguestfs detect this? Ideally
we would check somehow, and show the error message only when not
supported. Otherwise the alternative is simply unconditionally enable
discard for "parallels" disk images, although I don't know what would
happen when using versions of Virtuozzo older than 7.0.11.
Any Virtuozzo guy that can provide more insight?
--
Pino Toscano
6:59 a.m.
On Fri, Sep 27, 2019 at 12:00:58PM +0200, Pino Toscano wrote:
On Thursday, 26 September 2019 16:29:46 CEST Jonathan Wright wrote:
> virt-sparsify: error: libguestfs error: discard cannot be enabled on this
> drive: qemu does not support discard for '*parallels*' format files
Correct, this is because we have the following function to determine
whether it is supported:
https://github.com/libguestfs/libguestfs/blob/02890096d55eaee66c1e6ed34fc...
In a nutshell:
- raw supported with qemu >= 1.5
- qcow2 supported with qemu >= 1.6
- any other format is not supported
I wonder if it should just try to attach the image with discard=unmap
blockdev option, and bail out if that fails. This will allow to support
any image format where the capability is present in QEMU (ATM these
appear to be just qcow2 and raw format drivers but there are also a few
protocol drivers (iscsi, nbd, sheepdog, gluster) which can be relevant
for virt-sparsify too).
So we check based on the version of qemu currently.
> Since Virtuozzo 7.0.11 discard is officially supported for ploop images
> and I've mounted them with discard and confirmed this functionality
> works as expected. Would it be possible to update libguestfs to be
> aware of this support so the --inplace flag will work?
>
> https://virtuozzosupport.force.com/s/article/VZA-2019-059
This leads me to the question: how can libguestfs detect this? Ideally
we would check somehow, and show the error message only when not
supported. Otherwise the alternative is simply unconditionally enable
discard for "parallels" disk images, although I don't know what would
happen when using versions of Virtuozzo older than 7.0.11.
Please see my other message in this thread. This is not a property of
the image format, but that of the driver. And the driver in QEMU hasn't
changed so libguestfs doesn't need to adjust. If discard support is
ever added to the QEMU parallels format driver, libguestfs will be able
to test for it in a way similar to what it does for qcow2 and raw.
Meanwhile there's a workaround to achieve the same effect with a
different tool.
Roman.
6:38 a.m.
On Thu, Sep 26, 2019 at 09:29:46AM -0500, Jonathan Wright wrote:
virt-sparsify: error: libguestfs error: discard cannot be enabled on
this
drive: qemu does not support discard for '*parallels*' format files
Since Virtuozzo 7.0.11 discard is officially supported for ploop images and
I've mounted them with discard and confirmed this functionality works as
expected. Would it be possible to update libguestfs to be aware of this
support so the --inplace flag will work?
libguestfs does its work by attaching the image to a virtual machine
running in QEMU. So the ability of libguestfs to sparsify an image
depends on the QEMU driver for that image format to support discard.
Current parallels format driver in QEMU doesn't support it, and I'm
unaware of anyone working on it.
https://virtuozzosupport.force.com/s/article/VZA-2019-059
"Native discard support in ploop enabling automatic discard requests on all
ext4 filesystems over ploop block devices, except containers running on
Virtuozzo Storage."
This refers to ploop block device driver in Virtuozzo kernel. It allows
to present a parallels format image as a block device (similar to what
traditional loop devices do with raw images).
The feature you quote is that this driver gained the ability to handle
discard requests to the ploop device by punching holes in the underlying
image.
So in order to achieve the same effect as virt-sparsify, you need to
mount the image and call fstrim on the mountpoint.
Roman.
1883
days inactive
1884
days old
3 comments
3 participants
participants (3)
-
Jonathan Wright -
Pino Toscano -
Roman Kagan