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Re: [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical block sizes |
Date: |
Wed, 14 Dec 2011 13:05:19 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 |
Am 14.12.2011 12:47, schrieb Paolo Bonzini:
> On 12/14/2011 12:13 PM, Kevin Wolf wrote:
>> As we discussed before, the really interesting point here is defaults,
>> and whatever you choose to do is wrong in some respect.
>>
>> So it looks like you chose to make the virtual device default to the
>> host block size.
>
> ... wait wait, I default to 512. :)
>
> Here is the rationale. 512-over-4k may be slow, but is safe (but it is
> not slow if you align partitions properly). 4k-over-512 is unsafe. So,
> defaulting to 512 seemed the right thing after all.
Which means bounce buffers by default on 4k hosts. Is this going to
become our next cache=writethrough? At some point 4k disks will be in
wide use, but we'll still be stuck with a slow default of 512.
No matter what we decide here, I think it might really be a good idea to
save the block size in the image and use that as the default if nothing
else is specified on the command line.
Kevin
- [Qemu-devel] [PATCH 11/17] iscsi: save host block size, (continued)
- [Qemu-devel] [PATCH 11/17] iscsi: save host block size, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 12/17] block: allow waiting only for overlapping writes, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 10/17] raw: probe host_block_size, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 16/17] block: default physical block size to host block size, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 14/17] block: protect against "torn reads" for guest_block_size > host_block_size, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 15/17] block: align and serialize I/O when guest_block_size < host_block_size, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 13/17] block: allow waiting at arbitrary granularity, Paolo Bonzini, 2011/12/13
- [Qemu-devel] [PATCH 17/17] qemu-io: add blocksize argument to open, Paolo Bonzini, 2011/12/13
- Re: [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical block sizes, Kevin Wolf, 2011/12/14