Re: EXT4 vs LVM performance for VMs

[Theodore Ts'o <tytso@mit.edu>]

On Fri, Feb 12, 2016 at 03:13:26PM +0100, Premysl Kouril wrote:
> The performance results which I posted in my original post are after
> all the block allocation is done. In other words: on the testing
> machine we do a first fio run which writes and allocates the testing
> file (during this first run the fio performance is actually much worse
> that what I reported, single VM performance is about 700 IOPS) and
> then we do second fio run and we take the benchmark numbers from this
> second run.

So you allocated the file using a random write workload, so the file
was probably not very contiguous.  Whereas when you allocated the LVM
volume, it was probably allocated contiguously.  You can use the
filefrag tool to see how fragmented the file might be.

All of this being said, what are you trying to do?  If you are happy
using LVM, feel free to use it.  If there are specific features that
you want out of the file system, it's best that you explicitly
identify what you want, and so we can minimize the cost of the
features of what you want.

Cheers,

					- Ted