Growing file extent based iSCSI LUNs without truncate

[DaveY]

Is it safe (non-destructive, non-corruptive) to grow a file extent based iSCSI LUN by simply increasing the value of "Extent Size" from Sharing -> Block (iSCSI) -> Extents?

I did a quick test by bumping up a file extent from 50GB to 500GB and FN increased the underlying file to 500GB. My VMware host saw the new LUN size after a scan and I was able to in crease the VMFS without any issues.

FN documentation says to use truncate command line on the file extent itself and then setting the extent size to 0 (auto), but then I lose the ability to view the size of my LUNs from the webGUI.

Why is the WebGUI method not the preferred method? Just seems easier and I can still see the LUN size.

 

[cyberjock]

Not sure. But file based extents are just scary to me on 9.3. If you are on 9.3, there's major "free" performance benefits for using zvol based extents. Virtually nobody should be using file-based extents on 9.3, except for those that haven't had a chance to migrate yet. :P

 

[DaveY]

We chose file based extents based on many posts that it gives better performance than zvol. I didn't know there's a danger in using file based extents?!?? Do you have a link to where I can find more info on this? These LUNs are currently housing all of our corporate VMs.

 

[cyberjock]

Its not dangerous. It's just silly when you can see up to 300% better performance with zvols.

File based were the fastest prior to 9.3.

9.3 came with the ctl iSCSI initiator, which changed the behavior of what was fastest from file-based to zvol based.

 

[DaveY]

Thanks cyberjock. Haven't been following the FreeBSD/FreeNAS development that closely so completely missed the big code change memo. :)

Going to miss the ability to copy file extents over to another FreeNAS box and bringing up the iSCSI target elsewhere. ;) I'm not sure how I would even migrate the data for disaster recovery with a zvol; especially since FreeBSD still doesn't fully support VMFS and the fuse version is buggy.

 

[cyberjock]

You won't miss that.. just do ZFS replication. Zing!