Is ZLE doing anything for me?

[pixelking]

Is there any way to see what effect ZLE is having on an iSCSI volume? I have a 3TB ZFS volume that I have mounted to via iSCSI via a Windows Server 2008 iSCSI target. Server 2008 reports 860GB free, but FreeNAS reports 98% used. I'm in the middle of running "sdelete -c -s" on the drive, which should write zeros to all available space. Will ZLE then compress those zeros? If so, where will I see this, either in the web UI or in the CLI?

 

[pixelking]

Complete silence, eh? So either I've asked the dumbest question ever, or I've stumped everyone. Either way, not good!

 

[JaimieV]

Stumped, not dumb!

My backup NAS has ZLE compression turned on, while the primary does not - can't remember why I thought that was a good idea now, to be honest. Anyway, with 3.1 Tb of random crap, the backup is 2.8Tb disk space used.

According to http://hub.opensolaris.org/bin/view/Community+Group+zfs/faq , 'du' will report actual disk space used rather than the full size of the uncompressed file, but that might be a Solaris thing not BSD...

 

[pixelking]

Thanks, Jamie! Where do you see the 3.1tb vs 2.8tb numbers?

 

[pixelking]

Ok, I think I see what you're talking about. I ran

Code:

zfs list -r

and got back 2.64T USED and then I ran

Code:

du-hs /mnt/MyMount

and got back 2.7T, so I guess I'm not getting any compression yet. The sdelete command isn't finished running yet, so after it's done I'll update this post to say whether it's making a difference or not.

Thanks again!

 

[JaimieV]

Confirmed that du on FreeBSD does show the difference - I just du'd two trees on primary and backup, and the backup showed a good 30% reduction.

That was on a nicely compressible data set - documents. You'll see bugger all ZLE compression on movies/images/audio, as they're all directly compressed already.

 

[pixelking]

Good stuff!