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

Gary Buhrmaster gary.buhrmaster at gmail.com
Sun Jan 10 23:58:39 UTC 2021

On Sun, Jan 10, 2021 at 2:28 AM Richard Shaw <hobbes1069 at gmail.com> wrote:
> I'm looking at moving to a 4 drive raid1 array (and perhaps converting to raid5 later)

Be aware that raid5 (for large arrays) is not
a recommended solution due to the read errors
that (almost always) occur during reconstruction
if one has not been fastidious about background
scrubs because one of the disks being used for
recovery will itself get another read error (even
raid6 (raidz2 in ZFS terms) is encountering such
issues on arrays of common enterprise size(s)
these days, and is one of the reasons why
raidz3 exists if one needs to use a single array).

And last I knew btrfs raid5/6 still has some
really ugly failure modes, so, buyer beware.

That all said, as an experiment, it is likely

Now back to your original question.  Last
I was aware, the "usual" filesystem APIs
do not report the size available in a subvolume
based on the quota (although there are ways
to determine it).  It sounds like an interesting
addition to MythTV (I suspect patches to
properly calculate btrfs subvolume sizes
values would be reviewed, or, perhaps better
yet, changes to the kernel itself to "do the
expected thing").

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