[mythtv-users] Pre-recording Script?

[Jon Boehm]

It's a ST5000DM000.  I believe it is a shingled drive.  I'm actually
surprised at how often it does just fine.  I've got the Recording Pending
touch script enabled now.  We will see if that helps.  If not I have other
options.

Thanks

On Wed, Jan 10, 2018 at 4:30 PM, Stephen Worthington <
stephen_agent at jsw.gen.nz> wrote:

> On Wed, 10 Jan 2018 11:04:11 -0800, you wrote:
>
> >Hi
> >
> >I have a very slow drive and I allow it to spin down.  One of those drives
> >that are best used only for archiving.  Normally its fine for recordings,
> >but sometimes I get failed recording because, I theorize, that I have a
> >buffer overflow when the drive needs to spin up AND I have multiple
> >recordings starting at the same time.  My recording are coming from an
> >HDHomerun in h264.
> >
> >Is there a pre-recording script that can fire, say, 1-minute before a
> >recording is scheduled?  All I want it to do is touch a dummy file in the
> >recording directory.  I only have 1 recording directory so I don't even
> >need to think about which dir/drive needs to be touched.
> >
> >Thanks for the help
>
> Exactly what sort of drive is it?  If it is shingled drive, like the
> Seagate ST8000AS0002 8 Tbyte archive drives I use for my archiving,
> then spin up is not the only problem.  Shingled drives have to stop
> writing every so often in order to re-write tracks that get
> overwritten.  So they stop accepting write commands from the system
> for considerable periods of time (many seconds).  The time involved is
> way longer than the mythbackend and system buffers can cope with, so
> such drives can not be used for recording.
>
> How many recordings do you have starting at the same time?  When a
> recording starts, there is significant disk activity where the heads
> have to move back and forth to the system areas of the disk in order
> to set up the directory entries and space allocation for the files
> being opened.  Head movement takes a long time, and too much of it
> happening at once will mean that the heads do not get back to the
> correct location to write the next block of data for a recording
> before the buffers overflow.  If the problem is only at startup of
> multiple recordings, then you can manually fix that by telling one or
> more of the recordings to start early.  So if you are starting three
> recordings at the same time, you would set up override rules to start
> one recording two minutes early,one recording one minute early, and
> one recording would be left to start at the normal time.
>
> However, while recording, if you are recording to three files at once,
> the heads will be continually moving between the files.  There may be
> enough time for that most of the time, but when more space needs to be
> allocated for one of the files, the heads will then need to move to
> the system areas as well and that may cause a buffer overflow and loss
> of data in the middle of one or more of the recordings.
>
> As a rule of thumb, with modern hard drives, I would not want to have
> more than three recordings happening at once, and I have my system set
> up with enough recording drives (7) so that I have no more  than two
> recordings at once on any one drive.
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