[mythtv-users] Mythbackend recording glitches

[Stephen Worthington]

On Mon, 15 Oct 2018 19:26:10 -0700, you wrote:

>> What sort of partition(s) are you recording to?  Please post the fstab
>> line you are using for it, so we can see what options are being used.
>> If it is on the same drive as the system partition, please post the
>> fstab line for that too.
>>
>>
>It is straight default Mythbuntu 16.041 on a single 750G drive.  When I run
>out of ideas, I plan on buying a new 1T drive.
>
>dad at NewMyth:~$ more /etc/fstab
># /etc/fstab: static file system information.
>#
># Use 'blkid' to print the universally unique identifier for a
># device; this may be used with UUID= as a more robust way to name devices
># that works even if disks are added and removed. See fstab(5).
>#
># <file system> <mount point>   <type>  <options>       <dump>  <pass>
># / was on /dev/sda1 during installation
>UUID=863a7857-d97e-432f-be2a-aa6d00f4e75d /               ext4
>errors=remount-ro 0       1
># swap was on /dev/sda5 during installation
>UUID=e4227cca-c0b0-4da9-80ee-f6fd2d73abb9 none            swap    sw
>      0       0
>/dev/fd0        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0
>
>
>dad at NewMyth:/$ df
>Filesystem     1K-blocks      Used Available Use% Mounted on
>udev             1008340         0   1008340   0% /dev
>tmpfs             206196      6700    199496   4% /run
>/dev/sda1      718883112 269065760 413277092  40% /
>tmpfs            1030972     10196   1020776   1% /dev/shm
>tmpfs               5120         4      5116   1% /run/lock
>tmpfs            1030972         0   1030972   0% /sys/fs/cgroup
>tmpfs             206196         8    206188   1% /run/user/1000

A simple ext4 partition with the default options should work fine, but
you might like to try it with barriers off to see if that makes a
difference - barriers affect the write performance of large writes
more than anything else.  Turning barriers off permanently is probably
not a good idea as it makes you much more vulnerable to having the
partition damaged in a power failure or similar situation.  If you try
with the "barriers=0" setting, as you are using the boot drive, you
may also need to add a similar setting to the kernel options in grub.

Ext4 is OK for recordings, but XFS or JFS is considered better, as
they are more efficient at deleting huge files.  Ext3 is not
recommended unless you turn on the "slow delete" option, and even then
is not good.  I use JFS for all my recording partitions.

The partition is nowhere near full - a full partition causes the heads
to move around a lot and that can cause problems.

The best setup for MythTV is to have the system and database on an SSD
drive and the recordings going to their own (spinning rust) drive(s).
But I had my system working with recordings going to the same drive as
the system for a long time and it worked fine.  The disk was a
performance one though (Hitachi HDS723030ALA640 3 Tbyte 7200 rpm). And
I had the system on ext3 (and later ext4) and the recordings going to
a separate JFS partition on the same drive.

I am wondering what version of MythTV added the recordedseek table. If
you were previously using a version old enough that it did not have
recordedseek, then in the current version you will have a lot more
database activity as there are constant writes to recordedseek as each
recording file grows in size.

On the other end of things, have you tried getting a better signal in
the tuners by directly connecting only one HDHR to the aerial (no
splitter, with and without the amplifier)?  Does that help get a good
recording?  Are the aerial cables in good shape and solidly connected?

Is the splitter failing?  Is the amplifier failing?  The TV is getting
twice the signal of the tuners, as they are dual tuners and have an
extra splitter.  So the TV signal may be fine, but that is no
indication that the tuners will be.  And the TV tuner may be more
sensitive than the HDHR tuners as well.

Best practice with HDHR tuners is to have them on their own subnet
connected to a separate Ethernet port on the MythTV box.  But there
are many people using them happily without doing that.