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[Qemu-devel] Re: [PATCH v2] virtio-blk physical block size
From: |
Rusty Russell |
Subject: |
[Qemu-devel] Re: [PATCH v2] virtio-blk physical block size |
Date: |
Mon, 4 Jan 2010 13:38:51 +1030 |
User-agent: |
KMail/1.12.2 (Linux/2.6.31-16-generic; KDE/4.3.2; i686; ; ) |
On Tue, 29 Dec 2009 03:09:23 am Avi Kivity wrote:
> This patch adds a physical block size attribute to virtio disks,
> corresponding to /sys/devices/.../physical_block_size. It is defined as
> the request alignment which will not trigger RMW cycles. This can be
> important for modern disks which use 4K physical sectors (though they
> still support 512 logical sectors), and for file-backed disk images (which
> have both the underlying filesystem block size and their own allocation
> granularity to consider).
>
> Installers use this to align partitions to physical block boundaries.
>
> Note the spec already defined blk_size as the performance rather than
> minimum alignment. However the driver interpreted this as the logical
> block size, so I updated the spec to match the driver assuming the driver
> predates the spec and that this is an error.
I thought this was what I was doing, but I have shown over and over that
I have no idea about block devices.
Our current driver treats BLK_SIZE as the logical and physical size (see
blk_queue_logical_block_size).
I have no idea what "logical" vs. "physical" actually means. Anyone? Most
importantly, is it some Linux-internal difference or a real I/O-visible
distinction?
Rusty.
- [Qemu-devel] Re: [PATCH v2] virtio-blk physical block size,
Rusty Russell <=