I moved to DragonFly 2.10 over the past few days, and I tried out deduplication, to see what kind of results I would get. The procedure is outlined below. I’m using /home here as an example, just to reduce the amount of text pasted in.
/pfs/@@-1:00004 966000640 566434576 399566064 59% /home
Move my various Hammer pseudo-file systems to version 5, which supports deduplication.
# hammer version-upgrade /home 5
Issue a deduplication simulate command, to see what it guesses will be the savings:
# hammer dedup-simulate /home
Dedup-simulate /home: objspace 8000000000000000:0000 7fffffffffffffff:ffff pfs_id 4
Dedup-simulate /home succeeded
Simulated dedup ratio = 1.22
That ratio turned out to be pretty accurate for the actual deduplication. I didn’t time it, unfortunately. I don’t know if the time taken is proportional to the amount of deduplication or the total volume of data, though I suspect the latter.
# hammer dedup /home
Dedup /home: objspace 8000000000000000:0000 7fffffffffffffff:ffff pfs_id 4
Dedup /home succeeded
Dedup ratio = 1.22
462 GB referenced
378 GB allocated
14 MB skipped
6869 CRC collisions
0 SHA collisions
0 bigblock underflows
The end result?
/pfs/@@-1:00004 966000640 505887504 460113136 52% /home
That data space is shared across all file systems, and it’s a 1TB disk, so it’s 7%, or 70GB. I was hoping for more, but I don’t have any obviously duplicated data (no local mail store, no on-disk backups), so perhaps this is normal. 70GB that I didn’t have before is no bad thing, though.
Incidentally, I was able to upgrade my installed software from pkgsrc-2009Q4 to pkgsrc-2011Q1 entirely using pkg_radd -u <pkgname>. Remarkably quick and painless, though pkgin may have been able to do it even faster since it would pull from the same place.