Delta Backup / Snapshot / disk space

cgasser

Hi,

I am coming from VMware and I am new to XCP-NG. Regarding Delta backups I have one question:

It seems, that the first Delta Backup is doubling the required space on the LVM storage. Is that correct? Is there any way to avoid that? Any chance to do a differential backup to a NFS without doubling the required disk space? On the NAS (NFS) we have plenty of space, but the high performance (SSD, etc.) disk space is limited.

BR
C

cgasser

I found some useful information in this thread: https://xcp-ng.org/forum/post/22839
That basically anwers my question: On a LVM storage the amount of disk space doubles when creating the first snapshot. This is due to the fact that a LVM storage uses thick provisioning.

Learning: When installing a new server, be carefull if you choose LVM (thick provisioned; seems to be the default) or Local EXT (thin provisioned). According to some other posts, LVM seems to be a little bit more performant.

With VMware this is not the case. Even when using thick provisioning, you do not need double the disk space when creating a snap shot. This is even more critical, when you are running several VMs on a host and there is not a lot of disk space left. You can't make any snapshots then I guess. As you need at least double the amount of disk space than the VM that you want to snaphot already uses.

If anything from above is not correct, maybe someone with more experience can comment on that.

C

olivierlambert

It's only doubling during the snapshot, then the base copy will be deflated to the used space. But yes, at the exact moment you make the snap, you need the space available.

The performance penalty to use ext is almost invisible in real use cases.

cgasser

@olivierlambert Thank your for poiting this out! Very much apreciated!