Delta backup questions

Matteo

Hi. First of all, congratulations @vates for the product. I am using XO compiled from source. I'm trying to figure out how vm backup works. I have read the documentation, but I cannot find the information I am looking for. About delta backup:

During and after the backup, the disk where the virtual machines reside becomes almost full. This is because the disks are duplicated and the copy remains even after the backup is finished. Is this behavior normal? If so, this type of backup is practically unusable.
If I understand correctly, backups are compressed. Since the storage where I go to save the files is already compressed, I would like to disable xenorchestra compression. is it possible?
What happens if I select more than one destination storage? Are the backups duplicated or are they spread across the different storage?

Thanks

lawrencesystems

@Matteo

If the storage type you have the VM is thick provisioned it will take up more space. Use a thin provisioned storage for better storage efficiency
https://xcp-ng.org/docs/storage.html#storage-types

If you choose 2 storage destinations it will copy to each of them at the same time.

DustinB

@lawrencesystems said in Delta backup questions:

If you choose 2 storage destinations it will copy to each of them at the same time.

As a discrete backup that is saved to each location individually.

lawrencesystems

@DustinB said in Delta backup questions:

As a discrete backup that is saved to each location individually.

Yes, that is a more accurate statement.

Also, there is an option for doing Mirrored Backups:
https://xen-orchestra.com/docs/mirror_backup.html#mirror-backups

Matteo

@lawrencesystems Thank you for your answer. This is a big problem, because i need to use SAN storage, and so i can have thick VM only. I did not realize that the Snapshots was so big. what a pity...

DustinB

@Matteo said in Delta backup questions:

@lawrencesystems Thank you for your answer. This is a big problem, because i need to use SAN storage, and so i can have thick VM only. I did not realize that the Snapshots was so big. what a pity...

Are you backing up to your primary VM storage location as well? That generally is bad practice if it can be avoided.

lawrencesystems

@Matteo
You can use a SAN shared storage that is thin provisioned such as NFS.

Matteo

@DustinB no i'm trying a backup via nfs to another storage.

Matteo

@lawrencesystems you are right, but i'm using FC to have better performance.

olivierlambert

There's little to 0 difference in perfs between FC, iSCSI and NFS is real world scenario with XCP-ng.

Matteo

@olivierlambert Historically we have always used FC even on vmware, but I might consider using NFS. Thanks a lot to everyone

olivierlambert

You won't regret that, NFS is really nice

Matteo

@olivierlambert olivier another (maybe last ) question, just to understand the difference between thin and thick: If I had a thin VM, taking a snapshot, would it still eats double space? thanks

Danp

@Matteo said in Delta backup questions:

f I had a thin VM, taking a snapshot, would it still eats double space?

No, it would only use minimal space for the snapshot.

planedrop

I can confirm NFS is great on XCP-ng, would definitely encourage you got that direction, TBH FC and iSCSI are a tad outdated. There are still good use cases for them but NFS is the thing I'd always aim for in this setup.

And like @Danp said, if it's thin provisioned, then no it won't be using double the space.

olivierlambert

To be fair, the "doubling in space" is only temporary. As soon the snapshot is done, the base copy will be deflated to the really used space in the disk. But yes, the current active disk will be reserving the entire VDI disk size.

Matteo

But with delta backup in place i have double space allocated still after backup ending. is it normal? thanks

Matteo

e.g.

This snapshot is here from yesterday. I thought it was deleted when the backup was completed

olivierlambert

@Matteo No, except if your disk is full, deflate won't deflate anything. Also, what you see in XO by default doesn't reflect exactly, it's far more subtle than this. When you make a snap, you have 3 disks (here is thick case):

the base copy (read only, and deflated of the used blocks)
the active disk (full disk size allocated)
the snapshot itself (few KiB, just a pointer in time "linking" to the base copy)

Here with the 100GiB drive, if it's used at 50% (let's say), you will have 50GiB for the base copy and 100GiB for the active disk reserved on your thick storage.

Regarding the snapshot from yesterday, if the backup is done, you shouldn't have the disk still attached to the control domain.

Matteo

@olivierlambert i try to rebuild xo, and make a backup again. thanks to all