[mythtv-users] random livetv stalls

[Jean-Yves Avenard]

On 5 February 2014 13:48, Kevin Johnson <iitywygms at gmail.com> wrote:

>
> One other request.  If someone could point me to a how-to correctly reply to
> this list using gmail I will be eternally grateful.


simply reply at the bottom of the answer, not the top

> On Tue, Feb 4, 2014 at 5:55 PM, Kevin Johnson <iitywygms at gmail.com> wrote:
>> It seems like the frontend is waiting for info from the backend.  But I
>> really cant figure out what to look for.  And google search of  the above
>> errors shows very little.
>>
>> Could this be a i/o error with one of the drives?  If so, how do I test?
>> If not, any ideas where I should start looking?
>> Thanks to all.

Having been through this myself, I can guarantee you that it is always
disk related....

When you are playing from liveTV there are two things happening
simultaneously from the backend.

First is the recorder writing to the disk: that's thread #1
Then you have thread #2 handling request from the frontend and
requesting data; that is reading the data from the disk.

So one process of the backend write on disk, while another process
read from disk. You have a long delay occurring there, from your log,
it takes over 6s between the time the backend write to the disk, and
the reader reads that data. That's way too much. For information, you
get a warning that it's too low if it takes more than 0.2s.

After 10s waiting for sufficient data the reader on the backend will abort.
If it takes more than 16s to read a block of data, it will also abort.

Now how the frontend handle it when the backend abort is very poor.
The frontend usually will just appear to be locked. After a little
while you can exit it by pressing the exit key.

I guess, optimisation could be done, so if the frontend is watching
liveTV we don't have to wait for the backend to finish writing data to
disk before reading from disk once again and directly transfer it
right away to the client.

But at this stage, the design doesn't allow for it.

In the mean time, you need to identify where the bottleneck is. If you
are using NFS , check the mounting option (that's the issue I was
having), if using a RAID array, check the smart status to make sure
you don't have a disk dying that is slowing everything down.

Make sure your database isn't on the same disks where you are writing
your recordings and not on a RAID array. that has proven to often be
the reason for having massive speed slowdowns with disks