[mythtv-users] Delete files slowly

Michael T. Dean mtdean at thirdcontact.com
Tue Jan 26 05:31:37 UTC 2010


On 01/25/2010 08:32 PM, Greg Oliver wrote:
> I just noticed that while I have the setting to delete files slowly,
> and recording, it records faster than it deletes.
>
> Is there logic in this setting, or can I assume that it will always
> delete slower than 19mb/s (1 tuner)..  I guess ultimately I would hate
> to have frame loss because it is clearing disk space too slowly, but I
> am not familiar with the logic.  It may very well delete much faster
> as the available space gets lower, etc..
>   

Greg,

It turns out that we used to have a minimum truncate rate of 8MiB/sec
and would use that value or 120% the max recording bitrate (combined max
bitrate of all cards), whichever was higher.  Before 0.21 was released,
we removed the minimum truncate rate, so now do 120% ATSC max bitrate *
number of cards (basically 2.78MiB/sec/card (including "virtual" cards
for multirec)).

After some discussion on IRC, we may re-institute the minimum truncate
rate.  I plan to do some tests using different values for the truncate
rate (from the above 2.78MiB/sec (for the "minimal" one-card system) to
4MiB/sec to 8MiB/sec) and see if it has an effect on
http://svn.mythtv.org/trac/ticket/7315 (per discussion at and after
http://www.gossamer-threads.com/lists/mythtv/dev/416521#416521 ).  If
any of the values "fixes" #7315, I'll definitely institute a hard floor
higher than the current.

I won't be home until later this week, but if any enterprising users
want to run some tests for me, please feel free.  You can simply
hard-code values for min_tps at
http://svn.mythtv.org/trac/browser/trunk/mythtv/programs/mythbackend/mainserver.cpp#L1915
, i.e.:

const size_t min_tps = 1024 * 1024 * 8;

Also, do you have any stats showing the record rate and the delete
rate?  Are you sure some other process (or maybe MythTV log files)
wasn't what caused the disk usage to increase faster than free space? 
If so, those stats (and any info you may have on why the 120% ATSC max
bitrate * number of cards didn't work for you) would be very useful.

If it is deleting too slowly, can you please try running mythbackend
with a -v important,general,file (ideally logging to a different file
system :) so we can see whether it's actually able to do 2 truncates per
second or if there's an I/O wait issue or something slowing your truncates.

Thanks for the question/spurring the discussion.  :)

Mike


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