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Re: [Qemu-devel] [PATCHv3 1.8 8/9] qemu-img: increase min_sparse to 128
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From: |
Eric Blake |
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Subject: |
Re: [Qemu-devel] [PATCHv3 1.8 8/9] qemu-img: increase min_sparse to 128 sectors (64kb) |
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Date: |
Wed, 04 Dec 2013 19:12:15 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 |
On 12/04/2013 09:46 AM, Peter Lieven wrote:
>> I guess a sane size would be cluster size. For a raw file 4 KB is
>> reasonable since that's the file system block size.
> in case of iscsi the cluster size could be much too high as for example
> my storage has a cluster_size of 15MB.
>>
>> Is it necessary to increase to 64 KB here?
> No, its indepent of the rest. Paolo suggested to increase it and I can confirm
> that for my usage case its faster than 4K.
At least on NTFS file systems, 64k is the minimum size of a hole in a
sparse file. While many file systems support smaller holes, there are
definitely systems where trying to detect smaller holes only results in
wasted efforts. Is it worth making the default dynamic based on stat()
information regarding optimum IO size for the given destination file system?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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