Re: [linux-lvm] LVM performance vs direct dm-thin

From: Demi Marie Obenour <demi@invisiblethingslab.com>
To: LVM general discussion and development <linux-lvm@redhat.com>
Cc: "Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
	"Zdenek Kabelac" <zdenek.kabelac@gmail.com>
Subject: Re: [linux-lvm] LVM performance vs direct dm-thin
Date: Sun, 30 Jan 2022 17:14:43 -0500	[thread overview]
Message-ID: <YfcN6KHxLe3/krTX@itl-email> (raw)
In-Reply-To: <30ba3f0683afb9c3b60d96ac0019ced4ce9bb5b8.camel@gathman.org>

[-- Attachment #1.1: Type: text/plain, Size: 1945 bytes --]

On Sun, Jan 30, 2022 at 04:39:30PM -0500, Stuart D. Gathman wrote:
> On Sun, 2022-01-30 at 11:45 -0500, Demi Marie Obenour wrote:
> > On Sun, Jan 30, 2022 at 11:52:52AM +0100, Zdenek Kabelac wrote:
> > > 
> > 
> > > Since you mentioned ZFS - you might want focus on using 'ZFS-only'
> > > solution.
> > > Combining  ZFS or Btrfs with lvm2 is always going to be a painful
> > > way as
> > > those filesystems have their own volume management.
> > 
> > Absolutely!  That said, I do wonder what your thoughts on using loop
> > devices for VM storage are.  I know they are slower than thin
> > volumes,
> > but they are also much easier to manage, since they are just ordinary
> > disk files.  Any filesystem with reflink can provide the needed
> > copy-on-write support.
> 
> I use loop devices for test cases - especially with simulated IO
> errors.  Devs really appreciate having an easy reproducer for
> database/filesystem bugs (which often involve handling of IO errors). 
> But not for production VMs.
> 
> I use LVM as flexible partitions (i.e. only classic LVs, no thin pool).
> Classic LVs perform like partitions, literally using the same driver
> (device mapper) with a small number of extents, and are if anything
> more recoverable than partition tables.  We used to put LVM on bare
> drives (like AIX did) - who needs a partition table?  But on Wintel,
> you need a partition table for EFI and so that alien operating systems
> know there is something already on a disk.
> 
> Your VM usage is different from ours - you seem to need to clone and
> activate a VM quickly (like a vps provider might need to do).  We
> generally have to buy more RAM to add a new VM :-), so performance of
> creating a new LV is the least of our worries.

To put it mildly, yes :).  Ideally we could get VM boot time down to
100ms or lower.

-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[-- Attachment #2: Type: text/plain, Size: 201 bytes --]

_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/