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Re: [linux-lvm] Data deduplication for Linux : lessfs

On 24. juni. 2009, at 21.25, Mark Ruijter wrote:

Hi Roy,

It's a good idea, but given the current traffic on the lessfs mailing list, I'm not sure if much work is done. I have been a member of that list since June 1 and haven't received more than one message, which was the one I wrote myself.

Almost all the traffic is on the forum - open discussion.
Only one person posted to the mailing list. ;-)

Mailing lists are so much easier to use. Instead of visiting a bunch of websites, they all sit in my mailbox.

If done smartly, this may perhaps be possible, but the problem is the filesystem's metadata. Is this going to be dedup'ed? How much will this take? A simple backup will update atime on all the files backed up, and although atime isn't always wanted or needed, the problem occurs elsewhere.

Typically the meta data on production systems is approx 10%~20% of the deduplicated stored data. Stored data is on my systems 40x less then the data written to the filesystem.

The problems with metadata is not that they take up a lot of space, but that they are updated so regularly. As Greg Freemyer pointed out, relatime will help a lot, but still, deduplicating metadata may take up a serious amount of time because of the frequent updates.

Roy Sigurd Karlsbakk
(+47) 97542685
roy karlsbakk net
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