On 01/28/11 02:38 PM, Igor P wrote:
I created a zfs pool with dedup with the following settings:
zpool create data c8t1d0
zfs create data/shared
zfs set dedup=on data/shared
The thing I was wondering about was it seems like ZFS only dedup at the file
level and not the block. When I make multiple copies of a file to the store I
see an increase in the deup ratio, but when I copy similar files the ratio
stays at 1.00x.
Igor, ZFS does indeed perform dedup at the block level. Identical files
have identical blocks, of course, but "similar" files may have
differences such that data is inserted, deleted or changed so each block
is different. Same data has to be on the same block alignment to have
duplicate blocks. Also, it's important to have lots of RAM or high speed
devices to quickly access metadata, or removing data will take a lot of
time, so please use appropriately sized systems. That's been discussed a
lot on this list.
See Jeff Bonwick's blog for a very good description:
http://blogs.sun.com/bonwick/entry/zfs_dedup
I hope that's helpful,
Jeff (a different Jeff)
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