From: Jamie Lokier <jamie@shareable.org>
To: Avi Kivity <avi@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
qemu-devel@nongnu.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [Qemu-devel] Re: [PATCH v2] virtio-blk physical block size
Date: Tue, 5 Jan 2010 20:18:01 +0000 [thread overview]
Message-ID: <20100105201801.GK14376@shareable.org> (raw)
In-Reply-To: <4B4192A1.3030801@redhat.com>
Avi Kivity wrote:
> Physical block size is the what the logical block size would have been
> is software didn't suck. In theory they should be the same, but since
> compatibility reaons clamp the logical block size to 512, they have to
> differ. A disk may have a physical block size of 4096 and emulate
> logical block size of 512 on top of that using read-modify-write.
>
> Or so I understand it.
I think that's right, but a side effect is that if you get a power
failure during the read-modify-write, bytes anywhere in 4096 sector
may be incorrect, so journalling (etc.) needs to use 4096 byte blocks
for data integrity, even though the drive emulates smaller writes.
-- Jamie
next prev parent reply other threads:[~2010-01-05 20:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1262018363-15871-1-git-send-email-avi@redhat.com>
2010-01-04 3:08 ` [Qemu-devel] Re: [PATCH v2] virtio-blk physical block size Rusty Russell
2010-01-04 7:02 ` Avi Kivity
2010-01-05 20:18 ` Jamie Lokier [this message]
2010-01-04 8:30 ` Christoph Hellwig
2010-01-05 12:56 ` Rusty Russell
2010-01-05 12:58 ` Avi Kivity
2010-01-05 20:16 ` Jamie Lokier
2010-01-08 15:40 ` Christoph Hellwig
2010-01-10 12:35 ` Avi Kivity
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