I run a fileserver receiving backups of user containers. Two containers are poorly run docker systems with hundreds of near-identical directories not using overlayfs nor zfs clones. (I cannot touch the user's containers to remedy their use nor seem to educate them.)
I thought as a test to just copy the backup target zfs fs's on my fileserver to newly created fs's in the same pool but with dedup=on. The fs's are ~540GB and 630GB. Dedup is off for the pool and other fs's (compression is on).
I have done the copy, but now zpool list is showing a dedup of 2.93x on 25TB of data for the whole backup pool - when I've only copied about 1.15TB over for these two fs's.
Zpool list:
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
d 30.0T 25.7T 4.27T - - 41% 85% 2.92x ONLINE -
The zdb -DD output from this whole pool is:
bucket allocated referenced
______ ______________________________ ______________________________
refcnt blocks LSIZE PSIZE DSIZE blocks LSIZE PSIZE DSIZE
------ ------ ----- ----- ----- ------ ----- ----- -----
1 3.75M 454G 249G 250G 3.75M 454G 249G 250G
2 359K 41.0G 38.8G 39.2G 752K 84.9G 80.2G 81.1G
4 50.1K 4.43G 3.79G 3.94G 242K 21.2G 18.2G 18.9G
8 37.3K 2.98G 2.62G 2.77G 396K 31.3G 27.6G 29.2G
16 21.6K 1.63G 1.31G 1.39G 475K 34.9G 27.5G 29.4G
32 20.5K 918M 699M 854M 1.06M 46.8G 35.7G 44.0G
64 20.3K 1.07G 851M 991M 1.71M 93.6G 71.4G 82.8G
128 5.13K 341M 297M 327M 813K 55.3G 47.6G 51.8G
256 14.7K 725M 493M 592M 6.56M 328G 224G 267G
512 1.09K 7.44M 6.51M 21.3M 838K 4.80G 4.21G 15.4G
1K 119 300K 232K 1.88M 188K 427M 347M 2.95G
2K 22 65K 53K 352K 60.5K 172M 143M 968M
4K 9 33K 32.5K 144K 49.1K 150M 148M 786M
8K 3 2.50K 2.50K 48K 36.0K 29.3M 29.3M 576M
16K 5 2.50K 2.50K 80K 131K 65.7M 65.7M 2.05G
32K 1 512B 512B 16K 62.8K 31.4M 31.4M 1004M
64K 1 512B 512B 16K 90.9K 45.4M 45.4M 1.42G
Total 4.27M 507G 298G 301G 17.1M 1.13T 786G 880G
dedup = 2.93, compress = 1.47, copies = 1.12, dedup * compress / copies = 3.84
(One cannot run zdb -DD on a filesystem, just a whole pool.)
As for the used vs logicalused on the actual fs's, I see:
d/ntgor4 used 398G -
d/ntgor4 logicalused 542G -
d/ntgor5 used 528G -
d/ntgor5 logicalused 629G -
So not much savings at all, but the dedup value is quite high -- and the histogram suggests there is some large savings (esp. in the referenced # of blocks, esp. at 256 count).
Reading the histogram and checking PSIZE and DSIZE, Im assuming this only refers to those fs's with dedup - and not the whole pool -- and therefore zpool list's dedup factor does as well. (Unless it's including snapshots in the dedup?)
Can someone explain how to interpret this and why the dedup factor is so high?
