From: Jamie Lokier <jamie@shareable.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Javier Guerra <javier@guerrag.com>,
rusty@rustcorp.com.au, kvm@vger.kernel.org,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Re: Notes on block I/O data integrity
Date: Wed, 26 Aug 2009 19:57:55 +0100 [thread overview]
Message-ID: <20090826185755.GF25726@shareable.org> (raw)
In-Reply-To: <20090825193621.GA19778@lst.de>
Christoph Hellwig wrote:
> > what about LVM? iv'e read somewhere that it used to just eat barriers
> > used by XFS, making it less safe than simple partitions.
>
> Oh, any additional layers open another by cans of worms. On Linux until
> very recently using LVM or software raid means only disabled
> write caches are safe.
I believe that's still true except if there's more than one backing
drive, so software RAID still isn't safe. Did that change?
But even with barriers, software RAID may have a consistency problem
if one stripe is updated and the system fails before the matching
parity stripe is updated.
I've been told that some hardware RAID implementations implement a
kind of journalling to deal with this, but Linux software RAID does not.
-- Jamie
WARNING: multiple messages have this Message-ID (diff)
From: Jamie Lokier <jamie@shareable.org>
To: Christoph Hellwig <hch@lst.de>
Cc: rusty@rustcorp.com.au, qemu-devel@nongnu.org,
kvm@vger.kernel.org, Javier Guerra <javier@guerrag.com>
Subject: Re: [Qemu-devel] Re: Notes on block I/O data integrity
Date: Wed, 26 Aug 2009 19:57:55 +0100 [thread overview]
Message-ID: <20090826185755.GF25726@shareable.org> (raw)
In-Reply-To: <20090825193621.GA19778@lst.de>
Christoph Hellwig wrote:
> > what about LVM? iv'e read somewhere that it used to just eat barriers
> > used by XFS, making it less safe than simple partitions.
>
> Oh, any additional layers open another by cans of worms. On Linux until
> very recently using LVM or software raid means only disabled
> write caches are safe.
I believe that's still true except if there's more than one backing
drive, so software RAID still isn't safe. Did that change?
But even with barriers, software RAID may have a consistency problem
if one stripe is updated and the system fails before the matching
parity stripe is updated.
I've been told that some hardware RAID implementations implement a
kind of journalling to deal with this, but Linux software RAID does not.
-- Jamie
next prev parent reply other threads:[~2009-08-26 18:57 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-25 18:11 Notes on block I/O data integrity Christoph Hellwig
2009-08-25 18:11 ` [Qemu-devel] " Christoph Hellwig
2009-08-25 19:33 ` Javier Guerra
2009-08-25 19:33 ` [Qemu-devel] " Javier Guerra
2009-08-25 19:36 ` Christoph Hellwig
2009-08-25 19:36 ` [Qemu-devel] " Christoph Hellwig
2009-08-26 18:57 ` Jamie Lokier [this message]
2009-08-26 18:57 ` Jamie Lokier
2009-08-26 22:17 ` Christoph Hellwig
2009-08-26 22:17 ` Christoph Hellwig
2009-08-27 9:00 ` Jamie Lokier
2009-08-25 20:25 ` Nikola Ciprich
2009-08-25 20:25 ` [Qemu-devel] " Nikola Ciprich
2009-08-26 18:55 ` Jamie Lokier
2009-08-26 18:55 ` Jamie Lokier
2009-08-27 0:15 ` Christoph Hellwig
2009-08-27 0:15 ` [Qemu-devel] " Christoph Hellwig
2009-08-27 10:51 ` Rusty Russell
2009-08-27 10:51 ` [Qemu-devel] " Rusty Russell
2009-08-27 13:42 ` Christoph Hellwig
2009-08-27 13:42 ` [Qemu-devel] " Christoph Hellwig
2009-08-28 2:03 ` Rusty Russell
2009-08-28 2:03 ` [Qemu-devel] " Rusty Russell
2009-08-27 14:09 ` [Qemu-devel] " Jamie Lokier
2009-08-27 14:09 ` Jamie Lokier
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