XO cant Snapshot itself ?

olivierlambert

And how one would snapshot a physical disk?

Meth0d

@olivierlambert Well its virtual disk is located on a local attached 8TB Disk .....

olivierlambert

I suppose the xoa backup hdd is a raw virtual drive, isn't it?

Meth0d

@olivierlambert Yes i think it is, if i remember correct that was the only way to add +4TB drives ?
I just tested to do a snapshot from another VM on that disk, that works.

olivierlambert

Yes, because on your other VMs, you aren't using a raw VDI RAW doesn't support snapshots, as explained in our doc: https://docs.xcp-ng.org/storage/#using-raw-format

Meth0d

@olivierlambert Okay but obviously i can create snapshots on the RAW SR (here OPensense in the screenshot above). So this is a should but bould sometiomes does work situation ?-)

olivierlambert

Are you sure? It seems you did a snapshot on non-raw VM disk, which is OK. If you do a VM.snapshot, it will individually snapshot ALL the VM disk, including the raw ones. And this is when it breaks.

I would be very happy to get snapshots on raw drives, but it's not physically possible with SMAPIv1.

Meth0d

@olivierlambert maybe i missunderstood things, the RAW Disk from my XO VM is the 7TB data disk "[NOBAK] xoa_backup_hdd".
The system disk is "xoa_sda" is not RAW.

So i thought excluding the disk with "[NOBAK]" would make me able to snapshot the VM (system disk). So whenever you have attached a RAW device makes you unable to snapshot the VM.

Detaching it, taking a snapshot and reattaching it would work however?

olivierlambert

On XCP-ng 8.2: [NOBAK] will be only used by Xen Orchestra to NOT export the snapshot generated by VM.snapshot method.
On XCP-ng 8.3: [NOBAK] will be used by XO to exclude the disk from the VM.snaphot call during an XO backup (since we added that feature in XAPI ourselves)

In any case, a manual snapshot will snap all the drives.

Momi_V

You can do this on the cli (in 8.3) via

xe vm-snapshot new-name-label=newname uuid=vmUUID ignore-vdi-uuids=uuid1,uuid2,uuid3

It is currently not possible in Xen-Orchestra, see
https://xcp-ng.org/forum/topic/3607/snapshot-backup-exclude-additional-mounted-disk/8?_=1680267126156

Meth0d

Thanks for the heads up. A [NOSNAP] Feature sounds like a good idea though

olivierlambert

We have to discuss this internally with @julien-f

planedrop

FYI just for future things, a generally better way to make greater than 2TiB disks is to simply span them within the guest OS, so basically for 7TiB just make like 4 2TiB VHD's and then have the VM OS span those disks so they appear as a single disk within the VM.

I do this all the time, works super well and gives you the ability to still snapshot them, etc....

Meth0d

@planedrop are you using LVM for that or how are u doing that? I never bothered with the problem because i dont have enough local space for 8TB disk snapshots anyways.

planedrop

@Meth0d Format wise I am using EXT so it's thin provisioned, and since it's all thin provisioned, snapshots only take up the space of the changes to the disk, so you don't really need enough space for 8TB snapshots.

As for LVM, you mean in the VMs to manage spanning? So far I've only really had a need to go beyond 2TiB for Windows VMs so I'm just using NTFS with Windows Disk Manager for those spans. But I imagine you could do it with LVM in Linux, not sure if there are better options for it.

julien-f

@olivierlambert Does [NOSNAP] implies [NOBAK]?

If not, should we ignore [NOSNAP] when a snapshot is required to backup the VM?

olivierlambert

That's a good question and an important choice to make

IMHO, the principle of least surprise would tell to ignore [NOSNAP] during a backup. Because I'm afraid people would backup a VM with [NOSNAP] and expect it to be saved. That would be a bad surprise if not. What do you think?

julien-f

@olivierlambert I think that [NOSNAP] means that this VDI should not be snapshotted and that ignoring it during backup would be surprising.

But your point is valid too, I have no ideal solution, hence my question ^^

julien-f

I don't see a case where one would want [NOSNAP] but not [NOBAK]. Maybe we could require either none or both of them during a backup and not support one without the other?

olivierlambert

The situation I can have in mind:

you want your VM to be backup
when you do a manual snapshot, you don't want to snap a disk

But why doing this? I don't know, it's hard to predict the need for this… At least, if we choose to NOT doing a backup of this disk with NOSNAP, we MUST tell that clearly in the doc.