Inconsistent snapshots of running vm

[crazy-to-bike]

I use Proxmox 2.0 with 2 vm: A Debian 5 server and an IPcop.
On the Debian server there are running several databases (mySQL, postgres, OpenLDAP).

The running vm are backuped with the Proxmox backup function every night, using "snapshot".

Now I heard that ist's very likely that snapshots of vm with running databases cause inconsistent backups with loss of data. If that's true, snapshots of a running vm can't be used as reliable backup.

My questions to the developers of Proxmox:
1. Do you know about this problem and is it really likely?

2. A method to avoid this would be to also dump the memory contents to the snapshot, wouldn't it? Is this realized in the snapshot function of Proxmox?

3. If Proxmox snapshots can't be considered safe, would it solve the problem using "stop" as backup mode?

 

[dietmar]

1. Do you know about this problem and is it really likely?

Both mysql and postgres are transactional databases, so I don't think this problem exists. Worst case is that you need to run a database check. but you will never loose data.

 

[udo]

I use Proxmox 2.0 with 2 vm: A Debian 5 server and an IPcop.
On the Debian server there are running several databases (mySQL, postgres, OpenLDAP).

The running vm are backuped with the Proxmox backup function every night, using "snapshot".

Now I heard that ist's very likely that snapshots of vm with running databases cause inconsistent backups with loss of data. If that's true, snapshots of a running vm can't be used as reliable backup.

My questions to the developers of Proxmox:
1. Do you know about this problem and is it really likely?

2. A method to avoid this would be to also dump the memory contents to the snapshot, wouldn't it? Is this realized in the snapshot function of Proxmox?

3. If Proxmox snapshots can't be considered safe, would it solve the problem using "stop" as backup mode?

Hi,
like Dietmar wrote are mysql and postgres very stable for this case - openldap isn't it! I use the pve-backup only for backup the basic system (once a week) and have an backup inside the vm every night (bacula). But also here, I do first an database dump. Esp. with openldap it's absolutly nessesary!!

But you can wrote your own backup-scripts, like stop db inside VM (and sync), create snapshot, start db inside VM, backup VM, remove snapshot.

Udo

 

[dietmar]

openldap isn't it!

Why do you think that? openldap comes with various DB back-ends, and AFAIK all of them can handle that case. Only the ldif back-end is problematic.

 

[dietmar]

But I agree that it is always a good idea to have a database dump of important data.

 

[crazy-to-bike]

thanks for your answers.

Is the memory content also backuped using the snapshot mode?

Or would it be better to make backups in the suspend mode as Udo wrote?

 

[udo]

Why do you think that? openldap comes with various DB back-ends, and AFAIK all of them can handle that case. Only the ldif back-end is problematic.

Hi,
due an bad experience with an broken ldap (vm) after the host had an kernel-panic. And the ldap wasn't changed at this time.

Ok, the statement openldap can handle that is to short. You have right the backend is the important factor. In this case it's was the "normal" berkeley db (hdb).

Perhaps, it's was only bad luck, but db-dumps makes sense

Udo

 

[udo]

Hi,
no - only the disk was saved.

To save the full VM, with memory and proccessor-state is an nice feature, but not implemented.

Udo

 

[crazy-to-bike]

Hi,
no - only the disk was saved.

To save the full VM, with memory and proccessor-state is an nice feature, but not implemented.

Udo

also in the suspend mode?