[CentOS] LVM hatred, was Re: /boot on a separate partition?

[Marko Vojinovic]

On Tue, 23 Jun 2015 18:42:13 -0700
Gordon Messmer <gordon.messmer at gmail.com> wrote:
> 
> I wondered the same thing, especially in the context of someone who 
> prefers virtual machines.  LV-backed VMs have *dramatically* better
> disk performance than file-backed VMs.

Ok, you made me curious. Just how dramatic can it be? From where I'm
sitting, a read/write to a disk takes the amount of time it takes, the
hardware has a certain physical speed, regardless of the presence of
LVM. What am I missing?

For concreteness, let's say I have a guest machine, with a
dedicated physical partition for it, on a single drive. Or, I have the
same thing, only the dedicated partition is inside LVM. Why is there a
performance difference, and how dramatic is it?

If you convince me, I might just change my opinion about LVM. :-)

Oh, and just please don't tell me that the load can be spread accross
two or more harddrives, cutting the file access by a factor of two (or
more). I can do that with raid, no need for LVM. Stick to a single
harddrive scenario, please.

Best, :-)
Marko