Re: [Xen-users] LVM vs img

[Tim Post <tim.post@xxxxxxxxxxxxxxx>]

There really isn't one good answer to this, it really depends on your
intended use and technical abilities of those who need to maintain th
LVM or partition backed VBD's are preferable for a few reasons, 

1 - File backed VBD's are typically kept grouped together on a larger
ext3 / ext2 partition. If your system has issues, inodes flood or too
many un-orderly reboots you risk losing all vbd's on the partition. 

I kind of like keeping each dom-u on its own VG or partition just to
keep it safely isolated. On systems that remain static where guests
never need to be re-sized, I just use physical ext3 partitions and
forget lvm altogether. Its a few less modules to load and makes
maintenance easy.

2 - There is a performance degradation using file backed vbd's once you
reach 15 - 20 of them, depending on your system and how fast the disks
are. Obviously 10krpm drives won't have as much of an issue as
EIDE/SATA, likewise a 10k rpm disk on a PIII would choke before a SATA
on a dual core Opteron.

Loops are quite handy for swap if on local disks.

Other things to think about are backup needs, more or less frequency
thereof and how to accomplish them. Lots of people like using lvm
snapshots to accomplish that, but if you can handle it within the dom-u
or are using some sort of raid I suppose it wouldn't be a deciding
factor. 

This assumes you have the luxury of knowing the expected use of what you
deploy prior to deploying it, in many cases (a good example being the
web hosting industry) you just *can't* adequately anticipate needs very
far ahead.

If in doubt, go with lvm.

Best,
-Tim
 
On Sat, 2006-10-21 at 10:20 +0200, Franck wrote:
> Hi all,
> 
> is guest OS more performant on LVM partition onstead of img mount file ?
> I'm using xen 2.0.7 with LVM xenU and all is good. Is it the same with
> 3.0.3 ?
> 
> Regards
> 
> Franck


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