Re: [PLUG] [plug-announce] TOMORROW - Tue, Apr 19, 2016: PLUG North - "Linux Containers" by Jason Plum and Rich Freeman (*6:30 pm* at CoreDial in Blue Bell)

["Keith C. Perry" <kperry@daotechnologies.com>]

Not sure what you mean by "revert to snapshot".  My read of this is that when you launch and ephemeral container that is the actually snapshot created.  Similar to creating and running off of a VM clone.  When you are done (i.e. shut down the container) any changes you made against the container are gone thus there are actually no changes written into the container path.  If you were to launch the container again as ephemeral it would have to redo any work you performed previously.

"In any case, certainly no harm in supporting both if it is practical. LVM is hardly agnostic though."

Well yea but that is like saying you can only do Linux stuff if run Linux  :)  To clarify, when I said agnostic I was referring to the LVM snapshot facility- that is what is agnostic since you can create snapshots for any file system.  I think it was a bad idea to require a file system that is not production ready.  Especially when we have a mature product like LVM.  I honestly would have said the same thing if they forced people to use ZFS (which also has an internal snapshot feature).  If you want people to adopt the new "thingy" then your best bet is to not have other requirements that people are less familiar with.  I see a use case for ephemeral containers but definitely not if I have to use BTRFS and since I brought it up, if it was ZFS I would still not be "happy" but at least in that case, we're talking about a stable file system available on Linux, even if it isn't widely used.

You're right, supporting both would be ideal but that's probably a monumental effort.

"I imagine it would be pretty painful to use multi-device support on btrfs in conjunction with LVM."

LVM now include md's functionality (it does the heavy lifting under the hood) and the current [Redhat] recommendation as I read it, is to use LVM for everything- there is no functional reason to use md anymore.  So, with LVM you could easily create and manage a multi-device system with whatever fs you wanted on top of it and still be able to snapshot.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 
Keith C. Perry, MS E.E. 
Owner, DAO Technologies LLC 
(O) +1.215.525.4165 x2033 
(M) +1.215.432.5167 
www.daotechnologies.com

----- Original Message -----
From: "Rich Freeman" <r-plug@thefreemanclan.net>
To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
Sent: Wednesday, April 20, 2016 8:03:58 PM
Subject: Re: [PLUG] [plug-announce] TOMORROW - Tue, Apr 19, 2016: PLUG North - "Linux Containers" by Jason Plum and Rich Freeman (*6:30 pm* at CoreDial in Blue Bell)

On Wed, Apr 20, 2016 at 3:37 PM, Keith C. Perry
<kperry@daotechnologies.com> wrote:
> Failed to create snapshot /.#machine.4fdf96bbc0c40191 from /: Inappropriate ioctl for device
>
> This is indeed not using btrfs.  This seems like a design mistake since it forces the use of a particular filesystem which for now is not even production quality.  A more agnostic and production quality requirement would have been to hook into LVM and use its snap-shotting facilities.  I suspect somewhere out there is a conversation about why this was not done but I didn't check.

With LVM can you easily revert to a snapshot?  I know in the past that
wasn't possible, but that could have changed.

In any case, certainly no harm in supporting both if it is practical.
LVM is hardly agnostic though.  You can only use LVM snapshots if you
use LVM, and there isn't much point in using LVM if you're using
btrfs.  I imagine it would be pretty painful to use multi-device
support on btrfs in conjunction with LVM.

-- 
Rich
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