----- Original Message -----
From: rsivak@xxxxxxxxxxxxx
To: "CentOS Mailing list" <centos@xxxxxxxxxx>
Sent: Thursday, December 6, 2007 11:18:16 AM (GMT+1000) Australia/Brisbane
Subject: Filesystem that doesn't store duplicate data
Is there such a filesystem available? It seems like it wouldn't be too hard to implement... Basically do things on a block by block basis. Store md5 of a block in the table, and when writing a new block, check if the md5 already exists and then point the new block to the old block. Since md5 is not guaranteed unique, might need to do a diff between the 2 blocks and if the blocks are indeed different, handle it somehow.
When modifying an existing block that has multiple pointers, copy the block and modify the new block.
I know I'm oversimplifying things a lot, but something like this could work, no? Would be a great filesystem to store backups on, or things like vmware volumes...
Russ
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You are describing what I understand to be 'Data De-duplication". It is all the rage for backups as it has the potential to decrease backup times and volumes by significant amounts. I went to a presentation by Avamar (a partner of EMC ?) regarding this technology and it seemed really nice for your typical windows file server. I suppose it effectively turns your data into 'single-instance' which is no bad thing. I suppose it could be useful for large database backups as well.
You'd think that using this technology on a live filesystem could incur a significant performance penalty due to all those calculations (fuse module anyone ?). Imagine a hardware optimized data de-duplication disk controller, similar to raid XOR optimized cpus. Now that would be cool. All it would need to store was meta-data when it had already seen the exact same block. I think fundamentally it is similar in result to on the fly disk compression.
Let us know when you have a beta to test !
8^)
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