[pve-devel] create snapshots

Alexandre DERUMIER aderumier at odiso.com
Fri Aug 31 13:38:06 CEST 2012


>>No, I meant a different issue. What if data is on the host/network cache? But I guess we 
>>can assume that an fsync on the iscsi connection makes sure that all data is written? 

for vmstate
-----------
-pause the vm
bdrv_flush_all, flush the datas (fsync), to it's waiting the datas are written to the stable storage.
(so that's datas are flushed from all the cache (guest + host) )

with novmstate + guest filesystem freeze with qemu-ga
-------------------------------------------------------
xfs_freeze do the same thing (fsync + stop new write to filesystem)




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

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Vendredi 31 Août 2012 13:22:29 
Objet: RE: [pve-devel] create snapshots 

> >>I wonder it is would be safe to call an external script to create the snapshot 
> there? 
> >>Or is there still some data in the qemu block driver cache, or the host 
> cache? 
> yes, I think taking snapshot don't flush datas. 
> rbd devs said me that we need to freeze the filesystem with qemu-ga if we 
> want to be sure that's all is fine. 
> (Or filesystem will do a fsck at start to correct the missing data with his 
> journal). 
> 
> But if we save the state, that's not a problem, as the vm will save the 
> missings data in the memory and will flush them when the vm will reload the 
> state. 

No, I meant a different issue. What if data is on the host/network cache? But I guess we 
can assume that an fsync on the iscsi connection makes sure that all data is written? 





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Alexandre D e rumier 

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