[CentOS] not using LVM for Linux VM guests?

Thu Nov 17 13:43:38 UTC 2011
Barry Brimer <lists at brimer.org>

On Thu, 17 Nov 2011, Smithies, Russell wrote:

> 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.
> -------------------------------------------------------------

One reason I choose to have separate filesystems which do use LVM instead 
of VMware disks is that I can use different mount options.  For example my 
/tmp filesystems usually get noexec,nodev,nosuid .. with one 
root filesystem that contains everything, you can't use mount options as 
effectively.  I also bind mount /var/tmp to /tmp for the same reason.