Does compression in ZFS improve performance

Does compression in ZFS improve performance

First I grabbed a bunch of files from out of my documents folder. Combination of pdf, docx, txt, sql, etc.. I just ket grabbing files until I got to 3.9GB. I then put them in a 7zip archive using no compression, store only. So nowIi have one single file called test that is 3.9GB in size. This is the file I tested with.

First test was to transfer the files from my SSD OS drive to the zpool called raid0. Btw it is not a raid0, it is simply two 500GB WD blue drives mirrored.  I use rsync --progress so i can see whats happening during the transfer. Results for no compression on zpool raid0:

[root@test raid0]# rsync --progress /root/test /raid0/test
test
  4190667460 100%  162.84MB/s    0:00:24 (xfer#1, to-check=0/1)

sent 4191179086 bytes  received 31 bytes  171068535.39 bytes/sec
total size is 4190667460  speedup is 1.00

As you can see I get 162.84MB/s transfer. Not bad

Next test is I remove the file from the zpool and turn on compression, and repeat transfer

[root@test raid0]# rm *
rm: remove regular file `test'? y
[root@test raid0]# zfs set compression=lz4 raid0
[root@test raid0]# ls
[root@test raid0]# rsync --progress /root/test /raid0/test
test
  4190667460 100%  176.71MB/s    0:00:22 (xfer#1, to-check=0/1)

sent 4191179086 bytes  received 31 bytes  186274627.42 bytes/sec
total size is 4190667460  speedup is 1.00

As you can see my transfer was s bit faster. This time 176MB/s.  I also checked my compression ratio after the transfer on the zpool.

[root@test raid0]# zfs get compressratio raid0
NAME   PROPERTY       VALUE  SOURCE
raid0  compressratio  1.19x  -

So yes I got better speed and saved disk space. A win win I would think. But that compression on the fly does cost. I am running this on an Intel i5-4690k CPU @3.50/4.0 GHZ with 16GB DDR3 1600 RAM (8GBx2). Granted I just eyeballed the CPU load in htop but without compression I was looking at approximately 20% load. With compression a whopping 40+%.

I added the third 500GB WD blue drive and did a bit more testing

In a 3 drive raid0 using three 500GB WD blue drives with no compression I got 300MB/s transfer speed from seperate SSD drive to zpool. Usable space 1.5TB. Can stand ZERO failed drives.

In a 3 drive raidz using three 500GB WD blue drives with no compression I got 260MB/s transfer speed from seperate SSD drive to zpool. Usable space 1TB, Can stand ONE failed drive.

In a 3 drive raidz2 using three 500GB WD blue drives with no compression I got 160MB/s transfer speed from seperate SSD drive to zpool. Usable space 500GB. Can stand TWO failed drives