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Re: [Qemu-devel] [RFC] Disk integrity in QEMU
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [RFC] Disk integrity in QEMU |
Date: |
Mon, 13 Oct 2008 18:11:39 +0200 |
Le jeudi 09 octobre 2008 à 12:00 -0500, Anthony Liguori a écrit :
[...]
> So to summarize, I think we should enable O_DSYNC by default to
> ensure
> that guest data integrity is not dependent on the host OS, and that
> practically speaking, cache=off is only useful for very specialized
> circumstances. Part of the patch I'll follow up with includes
> changes
> to the man page to document all of this for users.
perhaps I'm wrong but I think O_DSYNC (in fact O_SYNC for linux) will
impact host filesystem performance, at least with ext3, because the
synchronicity is done through the commit of the journal of the whole
filesystem:
see fs/ext3/file.c:ext3_file_write() (I've removed the comments here) :
...
if (file->f_flags & O_SYNC) {
if (!ext3_should_journal_data(inode))
return ret;
goto force_commit;
}
if (!IS_SYNC(inode))
return ret;
force_commit:
err = ext3_force_commit(inode->i_sb);
if (err)
return err;
return ret;
}
Moreover, the real behavior depends on the type of the journaling system
you use...
Regards,
Laurent
--
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"La perfection est atteinte non quand il ne reste rien à
ajouter mais quand il ne reste rien à enlever." Saint Exupéry
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, (continued)
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Jens Axboe, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Jens Axboe, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/20
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, M. Warner Losh, 2008/10/19
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/19
Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Fabrice Bellard, 2008/10/10
Re: [Qemu-devel] [RFC] Disk integrity in QEMU,
Laurent Vivier <=
[Qemu-devel] Re: [RFC] Disk integrity in QEMU, Ryan Harper, 2008/10/13