[mythtv-users] Manage recording storage group with btrfs subvolume

[David Hampton]

On Fri, 2021-01-29 at 12:20 -0500, David Hampton wrote:
> On Wed, 2021-01-13 at 08:16 -0600, Richard Shaw wrote:
> > On Sun, Jan 10, 2021 at 9:25 AM David Hampton
> > <mythtv at love2code.net>
> > wrote:
> > > On Sun, 2021-01-10 at 19:21 +0800, James Linder wrote:
> > > > 
> > > > 
> > > > > On 10 Jan 2021, at 6:06 pm, Mike Perkins <
> > > > > mikep at randomtraveller.org.uk> wrote:
> > > > > 
> > > > > On 10/01/2021 02:27, Richard Shaw wrote:
> > > > > > I'm looking at moving to a 4 drive raid1 array (and perhaps
> > > > > > converting to
> > > > > > raid5 later) btrfs array. Most of the space will be used
> > > > > > for
> > > > > > media but I
> > > > > > want to keep 1TB for recordings.
> > > > > > The problem is that btrfs will share free space among
> > > subvolumes
> > > > > > by default
> > > > > > and I don't know if there is  a quota method that will
> > > > > > limit
> > > free
> > > > > > space
> > > > > > reporting so that the backend will expire recordings
> > > > > > properly
> > > > > > like on a
> > > > > > dedicated filesystem.
> > > > > > Anyone else run into this and have a solution?
> > > > > I run my "raid" volumes under LVM. That way I can allocate
> > > discrete
> > > > > volumes[1] to each function and the free space is not shared
> > > > > between them.
> > > > > 
> > > > > [1] Each volume can them be formatted a different way as
> > > required.
> > > > 
> > > > Richard why would you not partiton your disks *exactly* as you
> > > want,
> > > > rather than what your vendor (suse ??) decided what was good
> > > > for
> > > most
> > > > people. When I looked I decided that btrfs was not what I
> > > > wanted
> > > on
> > > > my myth server
> > > 
> > > For an opposite viewpoint, I've been running a four drive btrfs
> > > raid-6
> > > setup for about a decade as my recordings storage volume, and
> > > have
> > > been
> > > very happy with it. I only have the one subvolume though, so I've
> > > never
> > > looked at the quota support.
> > > 
> > 
> > 
> > Thanks for the feedback, unfortunately your email ended up in my
> > spam
> > folder so I just read it.
> > 
> > Yes, I'm planning a 4 disk array which is all my case can hold and
> > I
> > plan to move my existing 2TB drive to my BackupPC server which
> > currently has a 1TB drive that is full.
> > 
> > Did you system cron or systemd timers to scrub the array on a
> > regular
> > basis as outlined here?
> > 
> >  
> > https://lore.kernel.org/linux-btrfs/20200627032414.GX10769@hungrycats.org/
> 
> Thanks for that pointer. I don't actually have regular scrubs set up
> at
> the moment. I need to to that. My array runs at about 50% usage, so I
> haven't had any of the out-of-space problems I had when trying to use
> btrfs on a 90-95% full drive on my work laptop.

FYI for your scrub scheduling purposes, a btrfs scrub on my set of 4TB
drives took over eight hours for each drive.

David