How to backup iSCSI data?

[poldas]

Hi,
I use FreeNAS like a iSCSI storage for XenServer. I've VMs on iSCSI storage and I'm afraid about data when something will happen with FreeNAS. Can I backup iSCSI file to another storage and restore it when something will go wrong? It would be great to use HA over two FreeNAS but I know that this functionality is available only on TrueNAS... Can I use rsync to copy iSCSI file and restore it when I will be in need? How can I protect my data stored on iSCSI?

 

[Robert Trevellyan]

In general, you can preserve whatever is in a dataset in FreeNAS using snapshots and replication.

 

[poldas]

Thank you for answer Robert.

I have 4 x 3TB SATA disks in RAID-10 - available space ~6 TB and actually 1 TB is busy.
1. How big will be snapshot from my storage?
2. It means that I should have second FreeNAS with the same configuration (4 x 3 TB in RAID-10) to store snapshosts?
3. Can I use the data stored on the second FreeNAS immediately or should I do something else. For example connect iSCSI LUN from second FreeNAS?

 

[jgreco]

I have 4 x 3TB SATA disks in RAID-10 - available space ~6 TB and actually 1 TB is busy.

Please use proper terminology to describe your setup. I'm guessing that you mean you have two mirror vdevs in your pool. Guessing is bad.

You can use snapshots and replication, or just snapshots if you prefer. Snapshots are stored as the set of changes between the time you make the snap and now, so if you took a snap yesterday and then 50GB was written to the pool, the size required to store the snapshot on the local system would be approximately 50GB. The replication size is slightly more complicated.

The downside to snapshots is that they're not guaranteed to give you a runnable VM image, since the image you get is kinda like turning off a running VM. It is a perfect disk image of a system that was powered on. For this reason, you might prefer to avail yourself of whatever technology Xen has to quiesce a VM and take a backup image, and then store the backup images. This means you are less likely to be able to use the data stored on the second filer immediately, but that those images are more likely to be successfully run.

Backups are never a totally happy thing for VM's.

 

[poldas]

Yes indeed I've striped two mirror vdevs

 

[Robert Trevellyan]

Thank you for answer Robert.

I have 4 x 3TB SATA disks in RAID-10 - available space ~6 TB and actually 1 TB is busy.
1. How big will be snapshot from my storage?
2. It means that I should have second FreeNAS with the same configuration (4 x 3 TB in RAID-10) to store snapshosts?
3. Can I use the data stored on the second FreeNAS immediately or should I do something else. For example connect iSCSI LUN from second FreeNAS?

jgreco is clearly far more knowledgable than I, but I can still say:

2. Not necessarily. If you choose the snapshots/replication solution, all you need is another system running a compatible version of ZFS. It needn't necessarily be FreeNAS, though that's probably the simplest solution. The vdev layout need not be the same, you just need enough capacity. Many times people on this forum state that it's acceptable to have less redundancy in a pool that's only for backup, and certainly you don't need maximum performance from a backup-only pool. Depending on your risk tolerance, and if you have suitable hardware, you can even use another pool on the same box.

Edited for layout.

 

[jgreco]

jgreco is clearly far more knowledgable than I, but I can still say:

Don't confuse post count for knowledge.

 

[Robert Trevellyan]

Don't confuse post count for knowledge.

Never! But I've been lurking here long enough to form opinions about which members know what they're talking about.

 

[jgreco]

Never! But I've been lurking here long enough to form opinions about which members know what they're talking about.

Well, I was impressed with the quality of your response to the poster. It's always pleasant to discover that there are knowledgeable lurkers out there in the audience.

 

[Mlovelace]

It looks like Xen can leverage windows VSS to take transactionally consistent snapshots of the guest VMs. You could store those Xen created snapshots in a separate dataset that is then replicated to another freenas or zfs server.

 

[jgreco]

For this reason, you might prefer to avail yourself of whatever technology Xen has to quiesce a VM and take a backup image, and then store the backup images.

It looks like Xen can leverage windows VSS to take transactionally consistent snapshots of the guest VMs. You could store those Xen created snapshots in a separate dataset that is then replicated to another freenas or zfs server.

As usual Mlovelace nails the details. I'm an old UNIX guy and can never remember the Windows stuff.