[mythtv-users] Storage directory file system: too easy to unmount?

[Stephen Worthington]

On Fri, 14 Feb 2020 10:34:04 -0600, you wrote:

>On 2/13/20 7:10 PM, Stephen Worthington wrote:
>> 
>> This is working as designed.  It is very useful to be able to unmount
>> drives that might be used by MythTV but are currently not.  I do it
>> all the time, but I have seven recording drives, so having one or
>> three unavailable does not cause problems.  
>
>I see. My MythTV backend is a mid-tower PC and doesn't have a lot of 
>internal hard drive slots so I've stuck with one recording drive.

Do you have any more SATA ports that you can use, even if there are no
drive slots?  My MythTV box is like that - it has an HTPC case with
only three drive slots, but I am running 7 recording drives off it.
Three are hanging out the back on internal SATA and power cables
pulled out through an empty card slot.  Another is running as a eSATA
drive in an external drive mount.  These pictures show the ones out
the back:

http://www.jsw.gen.nz/mythtv/20181221_125853.jpg
http://www.jsw.gen.nz/mythtv/20181221_125936.jpg

>I do have a Synology NAS that supports NFS and iSCSI. It's on the same 
>switch as my backend server; iperf3 shows maximum GigE throughput: 940 
>Mbits/sec. What do you think of using such a device for MythTV 
>recordings? Would NFS be OK or would iSCSI be preferred?

That sort of speed is fine for a recording drive.  There are faster
hard drives than 1 Gbit/s these days, but for a very long time MythTV
has worked with drives that are slower than that.  However, you do
need to be a bit careful with the Ethernet bandwidth.  If you use up
the bandwidth for other things (like copying a video file to the NAS),
even if it is going to a different NAS drive, you may cause recordings
to be damaged.

Working out what number and type of drives you need for MythTV is a
bit of an art.  With modern hard drives, my rule of thumb is that they
can support up to three recordings at once, but I prefer to only have
two at once so that I can be assured that I can play back a recording
at the same time.  The limiting factor is not the drive write speed,
but the time taken to move the heads from one point on the drive to
another.  When you are recording three programmes at once, the heads
need to be able to move between all three recordings and also the
system areas where the file sizes and extents are recorded, and to do
it fast enough that they arrive and start writing at each recording
before MythTV runs out of RAM buffers for that recording.  And the
worst case is that two recordings will be at opposite ends of the
drive, so the heads have to move the maximum possible distance between
them.

Another option is USB 3 drives.  Each USB 3 port can support an
external USB 3 drive mount with one recording drive in it.  A USB 3.1
port can support multiple drives, as long as each gets USB 3
bandwidth.  I use USB 3 drives on my laptop to record when I am away
from home.

>> If you have only one
>> recording drive, then you may want to write a monitoring script that
>> will let you know if it is unavailable.
>
>Thanks for the sample script!
>
>Dave