[mythtv-users] Use of fsync

[Rich Freeman]

On Tue, Oct 22, 2013 at 1:21 PM, Gary Buhrmaster
<gary.buhrmaster at gmail.com> wrote:
> Last I was reading the FreeBSD, illumos, and nexenta
> bug lists there are some interesting edge cases with ZFS
> and flash ZILs.  However, that is almost certainly going
> down a rat hole that only about a handful of us are likely
> interested in.

Agree.  In my case I'm writing to btrfs, but not with any kind of
flash cache.  Flash cache isn't really expected to improve write
performance for something like MythTV in any case - it is more
targeted at lots of small random writes and not large sequential
writes.

In all my past experience with RAID5+LVM+ext4 disabling mythtv's
fsyncs have only reduced problems associated with buffer overrun.
I've only been running it for a day on btrfs+RAID1.  It would not
surprise me if the right approach varies based on what else is going
on with the system, configuration, kernel tuning, etc.

The one thing I might look to do in the short term is to spawn
mythbackend using ionice's realtime priority.  If there is contention
for the disk, most other operations on my server aren't going to be
penalized by waiting the way mythtv will.

Rich