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Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication |
Date: |
Thu, 3 Jan 2013 13:39:48 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Jan 02, 2013 at 12:26:37PM -0600, Troy Benjegerdes wrote:
> The probability may be 'low' but it is not zero. Just because it's
> hard to calculate the hash doesn't mean you can't do it. If your
> input data is not random the probability of a hash collision is
> going to get scewed.
The cost of catching hash collisions is an extra read for every write.
It's possible to reduce this with a 2nd hash function and/or caching.
I'm not sure it's worth it given the extremely low probability of a hash
collision.
Venti is an example of an existing system where hash collisions were
ignored because the probability is so low. See 3.1. Choice of Hash
Function section:
http://plan9.bell-labs.com/sys/doc/venti/venti.html
Stefan
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, (continued)
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Troy Benjegerdes, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Benoît Canet, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Troy Benjegerdes, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Benoît Canet, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, ronnie sahlberg, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Benoît Canet, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Troy Benjegerdes, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, ronnie sahlberg, 2013/01/02
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Troy Benjegerdes, 2013/01/03
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Dietmar Maurer, 2013/01/04
- Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Stefan Hajnoczi, 2013/01/04
Re: [Qemu-devel] [RFC V4 00/30] QCOW2 deduplication, Benoît Canet, 2013/01/03