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Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format |
Date: |
Fri, 10 Sep 2010 15:52:03 +0200 |
User-agent: |
Mutt/1.3.28i |
On Fri, Sep 10, 2010 at 08:39:21AM -0500, Anthony Liguori wrote:
> You're hand waving to a dangerous degree here :-)
>
> TRIM in qcow2 would require the following sequence:
>
> 1) remove cluster from L2 table
> 2) sync()
> 3) reduce cluster reference count
> 4) sync()
>
> TRIM needs to be fast so this is not going to be acceptable. How do you
> solve it?
It's utterly slow in any real life SSD.
> For QED, TRIM requires:
>
> 1) remove cluster from L2 table
> 2) sync()
>
> In both cases, I'm assuming we lazily write the free list and have a way
> to detect unclean mounts. Unclean mounts require an fsck() and both
> qcow2 and qed require it.
If you do proper transactional metadata updates you can completely drop
the sync. TRIM / SCSI unmap are optimizations that can just be noops
without compromising data integrity.
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, (continued)
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Kevin Wolf, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Stefan Hajnoczi, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Stefan Hajnoczi, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Anthony Liguori, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format,
Christoph Hellwig <=
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Kevin Wolf, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Anthony Liguori, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Anthony Liguori, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Avi Kivity, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Anthony Liguori, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Kevin Wolf, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Anthony Liguori, 2010/09/10
- Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format, Kevin Wolf, 2010/09/13