Proxmox backup process

[vince17]

Hello, I have been lately trying to get a better understanding of the backup process in Proxmox, and I have been doing some tests from my end. I understand Qemu supports two types of backup - Internal and External.
In Internal an internal snapshot is created within the qcow2 file, but while backing up a proxmox Qemu VM I did a Qemu img info on the Qcow2 file and found no internal snapshots.
In external snapshots, the original VM Qcow2 file becomes the backing Qcow2 file and also a snapshot Qcow2 file is created. I used inotifywait to find out any new snapshot Qcow2 files but couldn't find any.
Another possibility I thought was that Proxmox would be using LVM snapshots, but while backing up using Proxmox no LVM snapshots were created. I also made sure that the vps is not suspended.
So I am confused how exactly the backup process works within Proxmox.

I need this information to make sure I am offering my customers a safe backed-up vps product. Thank you in advance for your help.

 

[tom]

check http://pve.proxmox.com/wiki/Backup_and_Restore

(there is also a link to git inside this wiki page, with very detailed description).

 

[vince17]

(there is also a link to git inside this wiki page, with very detailed description).

Thank you for your reply Tom, I can't find any git links within that Wiki page, can you please help me out with the link ? I have been working on this for the past 3 days without any result. Thank you again.

 

[tom]

Thank you for your reply Tom, I can't find any git links within that Wiki page, can you please help me out with the link ? I have been working on this for the past 3 days without any result. Thank you again.

its in the "Introduction" section on the end of the paragraph.

 

[vince17]

I am sorry for jumping the guns in my previous post, I found the link and also read the entire text document, thank you so much, everything was good and informative.
I read a particular line in the doc which says,

During backup we simply intercept writes, then read existing data and store that directly into the archive. After that we can continue the write.

I was wondering how exactly does it intercept the writes? If you have any information related to this, I would just need the basic idea of the working is all, Thanks Tom.

 

[dietmar]

I was wondering how exactly does it intercept the writes? If you have any information related to this

http://git.qemu.org/?p=qemu.git;a=b...6431711f85c544d32629dd6321823c4d2f31a;hb=HEAD

 

[vince17]

http://git.qemu.org/?p=qemu.git;a=b...6431711f85c544d32629dd6321823c4d2f31a;hb=HEAD

I am not a C level programmer. But it seems you guys have added a block level backup code. However I couldnt find any documentation on how to use this feature.
I searched the QEMU site and didnt find any docs on the above code.

Would appreciate if you could give some link to the docs on the code above as to how to use the feature.

 

[tom]

... how to use the feature.

click on "Backup" on our GUI - or what do you mean?

 

[vince17]

click on "Backup" on our GUI - or what do you mean?

I mean what command is used to invoke the backup code written by Dietmar.
As per the document : https://git.proxmox.com/?p=pve-qemu-kvm.git;a=blob;f=backup.txt

The backup method described is :
1) It needs a unique format to store which you made
2) During backup we simply intercept writes, then read existing data and store that directly into the archive.

The second part I believe is a QEMU code which is written by Dietmar.
Now the C Code (dietmar pointed) is the second part of the backup. I guess there must be a QMP call to QEMU to start intercepting writes. However I cant find any such documentation on QEMUs website to intercept writes to make sure the backup method made by Proxmox is cool.

I am not saying Proxmox's backup is not working. But I need to be sure its a efficient method and its really ignited my curiosity at the same time.

 

[vince17]

@Dietmar / @tom would really appreciate if you guys could help me with my curiosity.

 

[tom]

@Dietmar / @tom would really appreciate if you guys could help me with my curiosity.

What curiosity? You got all available information about our backup and the link to the code, so what question is open?

 

[vince17]

What curiosity? You got all available information about our backup and the link to the code, so what question is open?

I dont have this bit :
"During backup we simply intercept writes, then read existing data and store that directly into the archive."

Is there a QMP command to initiate that in QEMU ?

 

[dietmar]

Is there a QMP command to initiate that in QEMU ?

Yes - we apply several patches to qemu, see:

https://git.proxmox.com/?p=pve-qemu...e08fdc2cb82cca7df911067d49cfd8c5ce2bc;hb=HEAD