[mythtv-users] Storing recordings on a NAS via NFS (I/O concerns)

[Tom Hayward]

On Mon, Jun 1, 2015 at 5:24 AM, John McEntee <jmcentee9 at gmail.com> wrote:
>>
>> The NAS has a gigabit ethernet port but it's a few years old, and the
>> disks are Hitachi 7200 RPM. Do you think it will be up to the job? Is there
>> a test I could do to check before I head down this path?
>>
> You could create another storage group and mount point to the  QNAP TS-410
> NAS  and do some test recordings to that.
>
> In the UK a hour recording is 2GB, so I would say 800MB in 49 seconds has
> lots of spare bandwidth for recording.

In my experience, the IO problems that occur during recording are not
due to bandwidth, but seek latency. MythTV syncs recording data to
disk once per second for each recording (IIRC). If 8 programs are
recording, it will need to seek to 8 different disk positions per
second, and that assumes no fragmentation, commercial detection,
playback, or other disk activity. In RAID, (depending on the
controller) you will need to wait for the slowest disk to complete the
write.

I dedicate multiple physical disks to MythTV and try to limit to two
recordings per disk. MythTV will balance recordings between disks. I
have no IO problems with this setup. In prime time, we are often
recording three programs, commercial flagging two, and watching one.

https://www.mythtv.org/wiki/Storage_Groups#Storage_Group_Disk_Scheduler

Like John suggests, do some test recordings. See how many simultaneous
recordings you can send to the QNAP before it starts to miss writes.

Tom