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Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynami
From: |
Stefano Garzarella |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size |
Date: |
Tue, 23 Apr 2019 10:26:57 +0200 |
User-agent: |
NeoMutt/20180716 |
On Tue, Apr 23, 2019 at 09:56:19AM +0200, Kevin Wolf wrote:
> Am 19.04.2019 um 14:23 hat Stefano Garzarella geschrieben:
> > Hi Kevin,
> >
> > On Wed, Apr 17, 2019 at 10:04:43AM +0200, Kevin Wolf wrote:
> > > Am 17.04.2019 um 09:34 hat Stefano Garzarella geschrieben:
> > > > On Mon, Apr 15, 2019 at 10:04:52AM +0200, Kevin Wolf wrote:
> > > > >
> > > > > I think a potential actual use case could be persistent dirty bitmaps
> > > > > for incremental backup. Though maybe that would be better served by
> > > > > using the rbd image just as a raw external data file and keeping the
> > > > > qcow2 metadata on a filesystem.
> > > >
> > > > Thanks to point it out! I'll take a look to understand how to keep
> > > > metadata separated from the data.
> > >
> > > I'd consider the feature still experimental, but for local files, it
> > > works like this:
> > >
> > > qemu-img create -f qcow2 -o data_file=test.raw test.qcow2 4G
> > >
> > > And then just use test.qcow2. As long as you can put everything you need
> > > into an rbd URL, the same approach should work. Otherwise, you may need
> > > to use QMP blockdev-create on creation and possibly the data-file option
> > > of the qcow2 driver for opening.
> >
> > Very interesting, I'll try to add this support also in the rbd driver.
>
> I don't understand - what is the thing you want to add to the rbd driver?
> qcow2 doesn't need special protocol driver support for doing this, and I
> don't think the QEMU rbd driver has any metadata that could be split off.
>
Oh sorry, I didn't understand that was completely independent from the
protocol.
> > > > > How fast is rbd_resize()? Does automatically resizing for every write
> > > > > request actually work reasonably well in practice? If it does, there
> > > > > is
> > > > > probably little reason not to allow it, even if the use cases are
> > > > > rather
> > > > > obscure.
> > > >
> > > > I'll try to measure the percentage of the time spent in the rbd_resize.
> > > >
> > > > Another solution could be to pass to the rbd driver the virtual size of
> > > > the image and resize it only one time also if the preallocation is
> > > > disabled, because RBD will not allocate blocks but IIUC it only set the
> > > > max
> > > > size.
> > > >
> > > > Do you think make sense? Is it feasible?
> > >
> > > In theory yes, though it requires modification of every driver that
> > > should be usable together with rbd (i.e. ideally all of the drivers). If
> > > automatic resize works good enough, I'd prefer that
> >
> > I did some tests and it seems that the cost of rbd_resize() is
> > negligible. IIUC it only updates the metadata without allocating any
> > blocks (if we are growing, like that case).
> >
> > Anyway the automatic resize will not affect the current use-case (raw
> > images on rbd), where the file size is set during the creation, so I
> > think there should not be side effects with this patch.
>
> Okay, sounds good.
>
> > I'm also adding the support for preallocation (i.e. full) in the rbd
> > driver that can be useful for qcow2 images.
> >
> > If you prefer I can resend this patch with the preallocation series.
>
> Let's keep seperate things separate. Huge patch series are always harder
> to handle.
Okay, thanks for the suggestion!
Should this patch go through your tree?
Thanks,
Stefano
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, (continued)
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Jason Dillaman, 2019/04/11
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Stefano Garzarella, 2019/04/11
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Jason Dillaman, 2019/04/11
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Stefano Garzarella, 2019/04/14
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Jason Dillaman, 2019/04/14
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/15
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Stefano Garzarella, 2019/04/17
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/17
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Stefano Garzarella, 2019/04/19
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/23
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size,
Stefano Garzarella <=
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/23
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/29
- Re: [Qemu-block] [Qemu-devel] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Stefano Garzarella, 2019/04/29
Re: [Qemu-block] [PATCH RFC 1/1] block/rbd: increase dynamically the image size, Kevin Wolf, 2019/04/29