[pve-devel] snapshot improvements

Alexandre DERUMIER aderumier at odiso.com
Mon Sep 24 12:22:39 CEST 2012


>>I currently allocate am image equal to the size of the VM memory. 

>>Then I simply do an incremental state save (like a vm migration), and keep 
>>the VM running until (saved_bytes + remaining_bytes < available_space). 

do you think image = size of memory if enough ? (if we have some bytes more with incremental ?)

>>This is not perfect, but seems to work. But maybe we need to make 
>>that feature optional in future? 
I'll test it. (but it's a huge improvement, I can't pause vm in production)




Also, any problem if some datas in vmstate need to be flushed to disk ? 
I see that you have add a "use writeback cache" patch, maybe it's for that case ?
If yes, does it works with all devices (ide/scsi/virtio) ? (with any guest driver version)



----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Lundi 24 Septembre 2012 11:52:04 
Objet: RE: [pve-devel] snapshot improvements 

> How is it possible to save the vmstate if the vm is not paused ? (with a lot a 
> memory write access by example ?) 

I currently allocate am image equal to the size of the VM memory. 

Then I simply do an incremental state save (like a vm migration), and keep 
the VM running until (saved_bytes + remaining_bytes < available_space). 

This is not perfect, but seems to work. But maybe we need to make 
that feature optional in future? 

Another improvement would be to save VM state to absolute positions inside 
the state file. That way disk usage would be limited, and would use minimal 
space when file-system support sparse files. But this functionality would require 
much more work inside qemu code. 

- Dietmar 


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