[mythtv-users] autoexpire hell

[Stephen Worthington]

On Tue, 4 Feb 2025 14:24:27 +0800, you wrote:

>> On Feb 4, 2025, at 11:32, jam <jam at tigger.ws> wrote:
>> 
>> There is a long story involving dual usb tuners ...
>> 
>> I've setup another master backend with /store as the main directory
>> 
>> I'm restoring files and backups to rationalize everything.
>> 
>> My 4T /store is now 96% full (flash so the usual rules don't apply: keep your usage under (say) 80%)
>> 
>> I deleted junk-recordings to make space, but how do I force autoexpire to run?
>
>Peter I would be incredibly useful to have a button [ ] autoexpire now on webbackend.
>I peruse the API which IMHO is seriously deficiant:
>I would let to see
>GetFileList be able return the list of “deleted” group files, and a
>AutoExpire fileName.
>
>If anybody can correct me, please do.
>I shall write a Qt file deletion app that may be of interest to Peter, or others. Concerted learning ahead

>James

Autoexpire normally happens when you run out of space on a recording
partition and mythbackend wants to record to it.  It also happens
regularly, but I am not sure how often.  Try:

grep -i autoexpire /var/log/mythtv/mythbackend.log

The amount of free space that autoexpire will create on each recording
partition seems to default to about 20 Gbytes.  I have never found the
exact number, but if I keep the free space above that, I do not get
any autoexpiring of recordings happening.  There may well be settings
for these things, but I have never found them.  To get mythbackend to
autoexpire down to 80% of 4 Tbytes, you would need to set the
autoexpire size to 240 Gbytes on that partition only (you would only
want 20 Gbytes on hard disk partitions).

The normal way to ensure that your flash has enough spare blocks so
that it can erase them in time for reuse is to only format 80% or 90%
of the flash drive into partitions accessible by the system.  This is
called "overprovisioning".  The remaining unparitioned space then
provides that many flash blocks that the flash's operating system can
use for its erased block queue, even when the rest of the flash is
full.  Since flashes assign the address of each block as required,
blocks in unformatted space are not left unused as they are on a hard
drive.  The flash operating system uses all of the blocks on the drive
and just changes the address as they go on and off the erased list.

See:

https://www.techtarget.com/searchstorage/definition/overprovisioning-SSD-overprovisioning

So you should not need to use the MythTV autoexpire to provide any
free blocks to keep the flash drive running at full speed.  The free
blocks should be provided via overprovisioning.