[pve-devel] qcow2 bench and speed optimisations

Alexandre DERUMIER aderumier at odiso.com
Fri Sep 14 08:55:05 CEST 2012


>>What performance to you get when you pre-allocate the raw file? 
I don't think we can preallocated a raw file. (the file is empty but have a size of xx giga)



some doc here from rehdat:
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Virtualization/3.0/html/Administration_Guide/Administration_Guide-Manage_Objects.html

Table 6.3. Permitted Storage Combinations
Storage	 Format	 Type	 Note

NFS or iSCSI/FCP	 Raw or Qcow2	 Sparse or Preallocated	
NFS	                 Raw	          Preallocated	          A file with an initial size which equals the amount of storage defined for the virtual disk, and has no formatting.
NFS	                 Raw	          Sparse	 A file with an initial size which is close to zero, and has no formatting.
NFS	                 Qcow2	          Sparse	 A file with an initial size which is close to zero, and has RAW formatting. Subsequent layers will be Qcow2 formatted.
SAN	                 Raw	           Preallocated	 A block device with an initial size which equals the amount of storage defined for the virtual disk, and has no formatting.
SAN	                 Qcow2	           Preallocated	 A block device with an initial size which equals the amount of storage defined for the virtual disk, and has qcow2 formatting.
SAN	                 Qcow2	          Sparse	 A block device with an initial size which is much smaller than the size defined for the VDisk (currently 1GB), and has Qcow2 formatting for which space is allocated as needed (currently in 1GB increments).


note : they seem to use qcow2 on top of iscsi block devices, so it should works with lvm too :)


----- 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 14 Septembre 2012 07:58:42 
Objet: RE: [pve-devel] qcow2 bench and speed optimisations 

> >>If so, we can do that by default, because metadata is small (128MB/TB). 
> Note that the size file is the full size of the disk (no sparse file). 

That is bad. 

What performance to you get when you pre-allocate the raw file? 


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