Increase size of a zfs-volume, delete -dataset

[drnicolas]

I hope I use the right words for all the zfs-stuff ...

A long time ago, I started experimenting with zfs and iscsi for my backup-program.

At the moment I have ...
1. A ZFS-volume sized 1.8T which is presented to BackupExec on a W2012-machine via iSCSI
2. I also have a ZFS-dataset which is accessible via a CIFS-share, limited to 1800Gb and it is compressed

Both are working fine, maybe they differ in speed. Actually I think, I don't need this "double-feature" anymore.

Is it better to keep the volume/iSCSI-construction or keep the CIFS-share/dataset?

In case you vote for the -volume/iSCSI - and this is the real question:
Can I INCREASE the size of the ZFS-volume without problems (I think of fragmentation). Of course the -dataset has to be emptied before.



THank you for your help ...

[drnicolas]

Noone here who can help me ?

[Onichan]

You can increase zvol's without issues. It doesn't zero fill a zvol so I don't see how expanding it would be any different than creating a new one. It will fragment over time like any disk will and since it's copy on write, anytime you write something it's going to write the new blocks to somewhere that probably isn't next to where the old data is, but there isn't anything you can do about that.

Anyways I personally prefer avoiding zvols just so the data isn't stuck in some giant "file" on the NAS side. With the files directly on the NAS in a dataset it allows you to copy/move/manage the individual files themselves without being required to go through a 2nd machine.

[drnicolas]

If I understand you right, you vote for NOT using a iSCSI/zvol-solution and prefer the zdataset/share-solution.

In fact, it sounds easier and safer to have all the files readable in a diretory tree on the NAS.
The iSCSI needs some "Target"-machine which "decodes" the iSCSI-Target; therefore the files are only readable on the "target", not on the NAS.
Are there any differences in Speed between the 2 variants?

What about a datastore for VMware ESXi/vsphere ?

[raulfg3]

iSCSI/zvol-solution better speed
zdataset/share-solution Normal speed

PD: iSCSI protocol is lightweight and have performance in mind.

[Onichan]

About the performance, that would depend. For simple setups or home use I would say SMB is faster if setup right. Since it's asynchronous it would have more random write IO and in my experience it has about as fast sequential writes as iSCSI over 1Gb. When you get into multiple NICs and multi-pathing or 10Gb then iSCSI can be faster sequential and faster IO.

For a datastore I don't think they support SMB so you have to use NFS or iSCSI. Which NFS is like SMB in the fact the files themselves are just on the NAS instead of in a LUN. Which to use is really depends, for home use again I would go with NFS for reasons I have already mentioned. For enterprise many people do go with iSCSI for performance reasons though NFS is pretty good nowadays, we actually use NFS at work.