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Re: [Qemu-devel] [RFC V3 01/24] qcow2: Add deduplication to the qcow2 sp
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC V3 01/24] qcow2: Add deduplication to the qcow2 specification. |
Date: |
Tue, 11 Dec 2012 16:03:16 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 |
On 11/26/2012 06:05 AM, Benoît Canet wrote:
> Signed-off-by: Benoit Canet <address@hidden>
> ---
> docs/specs/qcow2.txt | 33 ++++++++++++++++++++++++++++++++-
> 1 file changed, 32 insertions(+), 1 deletion(-)
>
In addition to Stefan's comments,
> @@ -159,6 +163,33 @@ the header extension data. Each entry look like this:
> terminated if it has full length)
>
>
> +== Deduplication ==
> +
> +The deduplication extension contains the offset and size of the deduplication
> +table.
> +
> + Byte 0 - 7: Offset
> +
> + 8 - 11: Size
> +
> +== Deduplication table ==
> +
> +The deduplication table contains 64 bits offsets to the level 2 deduplication
s/64 bits/64-bit/
> +table clusters.
> +Each entry of these clusters contains a 32 bytes SHA256 hash followed by the
s/32 bytes/32-byte/
> +64 bits logical offset of the first encountered block having this hash.
s/64 bits/64-bit/
> +
> +Entries in the deduplication table are orderered by physical cluster index.
s/orderered/ordered/
> +
> +The number of entries in an l2 deduplication table cluster is :
> +l2_dedup_cluster_entries = cluster_size / (32 + 8)
32+8 is not a power of two; what happens to the tail bytes at the end of
a cluster of entries? If you define them to be 0 now, you can use them
for possible extensions later.
> +
> +The index in the level 1 deduplication table is :
> +l1_dedup_index = physical_cluster_index / l2_dedup_cluster_entries
> +
> +The index in the level 2 deduplication table is:
> +l2_dedup_index = physical_cluster_index % l2_dedup_cluster_entries
> +
> == Host cluster management ==
>
> qcow2 manages the allocation of host clusters by maintaining a reference
> count
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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