[mythtv-users] Combined FE/BE using USB for all I/O?

[Yeechang Lee]

Stephen Worthington <stephen_agent at jsw.gen.nz> says:
> I would be wary of doing more than three recordings at a time on one
> hard disk.

[...]

> My rule of thumb is to have no more than two recordings at once per
> drive if possible.

This is why I contributed a patch--later added to 0.27--to the disk
scheduler's Balanced Disk I/O option
(<URL:http://www.mythtv.org/wiki/Storage_Group#Balanced_Disk_I.2FO>).
Balanced Free Space is usually the preferred option as it avoids the
"I added a new empty drive to my MythTV system but brand-new
recordings are still expiring almost immediately!" problem
(<URL:http://www.gossamer-threads.com/lists/mythtv/users/346903#346903>).
Using it means, however, that every recording that starts at a given
moment will go to the filesystem with the most free space.

This isn't a problem for most people, but can cause disk contention
issues for those with more than three tuners. I have five physical
tuners, for example, and with ATSC subchannels seven recordings can
simultaneously occur. It's possible for all seven to start at once,
and with Balanced Free Space they would *all* go to the single drive
with the most free space at that moment.

Balanced Disk I/O with my patch avoids this by having the system only
use free space to choose the filesystem to record to if other
determinants like whether that filesystem is already being recorded
to/played from are equal. In the above scenario with seven
simultaneous recordings starting at once, they will be spread out
among the filesystems with the most free space.