[CentOS] not using LVM for Linux VM guests?

Wed Nov 16 23:31:14 UTC 2011
James A. Peltier <jpeltier at sfu.ca>

We use who disk LVM on our VMs.  No partitioning except for the root disk which is separate for all our VMs.  Since for us the root disks are largely static and all other components are on the full disk LVM volumes growing them doesn't require a reboot at all.  Just rescan the scsi bus and resize.  Done!

----- Original Message -----
| I came across an old post comment yesterday (from
| http://echenh.blogspot.com/2010/04/how-to-extend-lvm-on-vmware-guest-os.html
| ) discussing the "hack" of LVM on Linux VM guests and whether it's
| better not to use it to simplify disk management.
| I've re-posted the comment below, does it sound reasonable? Is it
| better to not use LVM on Linux VM guests?
| --Russell
| -----------------------------------------------------------
| At my job, after doing the same kind of procedure graph, we began to
| ask ourselves, why are using a LVM on a Linux VM guests?
| Since we're no longer living in the physical OS world, we didn't need
| to use the OS hacks(LVM) to overcome physical disk limitations
| anymore.
| We decided to Just let the hypervisor and virtual storage do that work
| for us.
| For example, in our production setup (3 tier commerce with VMs for
| database , webserver, and appserver), we're see a great improvement in
| managability and performance (>10%) by just dropping LVM, and most
| partitions.
| In your example, the resize process is 7 functional steps:
| 1. Increase size of VMDK
| 2. In VM OS, Create Partition (??)
| 3. REBOOT (!!)
| 4. PVCreate
| 5. VGExtend
| 6. LVExtend
| 7. Resize2fs
| Going to a LVM/partition-less setup reduces expansion to 3 steps and
| we don't need to take the VM OS offline!
| 1. Increase size of VMDK
| 2- Inside the VM, OS, rescan the scsi drive with:'echo 1
| >/sys/class/scsi_device//rescan; dmesg' (dmesg will check that you
| drive isize has grown)
| 3- Resize2fs.
| Our current disk arrangement has 3 VM HD devices
| 0 - small device (100M) with a single BOOT partition
| 1 - entire device is /
| 2 - entire device is SWAP
| Doing this has simplified resizing so much, I now let the junior
| admins and my manager expand drive space as needed.
| It's also let's us really be spartan on space since expansion is so
| quick. Instead of increasing systems in 30-50GB chunks, we can do
| 10-15GB and let our rmonitoring system warn us when space gets tight.
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James A. Peltier
IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices
I will do the best I can with the talent I have