[pve-devel] KVM Live Backup performance

[Cesar Peschiera]

Right Alessandro, and now, thiese are my questions:

1- "KVM live Backup" with the new code of backup, will do write cache for 
use of the VM?
2- If the question above is correct, how much write cache will make this new 
code of backup?
And the question more important:
3- If the first question is correct, is possible to make a new code of "KVM 
live Backup" that don't make write cache for use of the VM and nor affect 
the I/O performance of the VM (always thinking that the VM is in High 
Availability)?

----- Original Message ----- 
From: "Alessandro Briosi" <ab1 at metalit.com>
To: "Dietmar Maurer" <dietmar at proxmox.com>; "Cesar Peschiera" 
<brain at click.com.py>; <pve-devel at pve.proxmox.com>
Sent: Tuesday, January 28, 2014 4:28 AM
Subject: Re: [pve-devel] KVM Live Backup performance


> Il 28/01/2014 06:52, Dietmar Maurer ha scritto:
>>> If is possible without lose performance into this VM, the write cache 
>>> for "KVM
>>> Live Backup" not must to execute it. In this mode the "KVM Live Backup" 
>>> will be
>>> fantastic.
>>
>> Sorry, but I do not really understand that question?
>>
>> We have done many improvement on backup code, so you should first test 
>> with the newest binaries
>> available on the 'pvetest' repository.
>>
>
> If I understood it correctly he is concerned about the new "KVM Live 
> Backup"
>
> He is complaining that the new code enables write cache during backup.
> If there's a VM which is running a database in an HA scenario, and for
> some reasons the VM/host crashes during the backup, the database would
> be inconsistent when started on another host, cause of the write cache.
>
> So he is asking if there's a way to disable/avoid KVM backup to use
> write cache.
>
> I have no idea if he's statement is correct though. Does really KVM
> backup enable write cache ?
>
> Alessandro
>