Re: [Xen-users] Xen Image File vs LVM

["Grant McWilliams" <grantmasterflash@xxxxxxxxx>]

On Thu, Jul 31, 2008 at 12:00 PM, Chris Edwards <cedwards@xxxxxxxxxxxxxxxx> wrote:

Hello,

 

I have been playing around with Xen for a few months now and I have not been able to find any information on the differences between storing a Xen guest OS as a image file or as a LVM.  Is there performance differences?  What are the pros and cons?

 

Thanks for any help.

 

---

 

Chris Edwards

 

Chris,

Following are two tests I did to check this very thing.  

Test 1 - Disk File

The disk image /dev/xvdb1 was mounted as /media/test1. The images itself was stored on a 500 GB SATA drive. The relevent numbers are highlighted in blue.

/dev/xvdb1            10317828    154236   9639476   2% /media/test1

 [root@localhost ~]# bonnie++ -s 2048 -d /media/test1 -u root

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
localhost.locald 2G  6065 15 70595 37 20649 2 26878 53 57270 0 135.8 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
16 17008 99 +++++ +++ 26079 90 16002 94 +++++ +++ 29094 99
localhost.localdomain,2G,6065,15,70595,37,20649,2,26878,53,57270,0,135.8,0,16,17008,99,+++++,+++,26079,90,16002,94,+++++,+++,29094,99 

 

Test 2 - LVM

The LVM Logical Volume was created on the same 500 GB SATA drive and mounted in the domU as /media/test2

/dev/xvdc             10321208    154236   9642684   2% /media/test2

[root@localhost ~]# bonnie++ -s 2048 -d /media/test2 -u root

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
localhost.locald 2G 34825 92 50898 26 24833 4 35920 69 77594 1 137.9 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
16 15556 92 +++++ +++ 26198 96 16281 98 +++++ +++ 28508 100
localhost.localdomain,2G,34825,92,50898,26,24833,4,35920,69,77594,1,137.9,0,16,15556,92,+++++,+++,26198,96,16281,98,+++++,+++,28508,100
INIT: version 2.86 reloading

 

LVM soundly trounced the disk image in Sequential Output - Per Chr by about 600% and bettered it by about 20-30% in the other tests. The one interesting thing though was Sequential Output - Block where the disk image pulled ahead of LVM by about 20%. This I can't account for and will need to retest because it doesn't make a lot of sense. All of the Sequential Create/Delete stats were within 10% of each other.

The advantage of files are you can use standard Linux copy and delete commands to manipulate them. The advantage of LVM is it's faster and you can benefit from LVMs ability to resize as well as create snapshots. You could of course do this with your disk file being on the Dom0's LVM setup too by utilizing the hosts LVM features.

Grant McWilliams

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