[mythtv-users] advice on recording direct to NAS

[Stephen Worthington]

On Sat, 23 May 2015 04:56:58 +0000, you wrote:

>On Fri, May 22, 2015 at 9:51 PM Mark Perkins <perkins1724 at hotmail.com>
>wrote:
>
>>  Hi all, looking for advice:
>>
>> Background: I’ve just lost a second HDD in 6months and its getting very,
>> very, very annoying.
>>
>> I have a NAS that would have capacity to record to, but have not done so
>> because of concern for failed recordings due to potential inconsistencies
>> in network and / or NAS performance. I run 4 HDD in my mythbackend
>> supporting 30tuners (nominal worst case 8 recordings at a time due to
>> overlap of pre/post roll).
>>
>> Does anyone record directly to a NAS folder? How did you share the folder
>> with your server? Does it work well? Do temporary spikes in network load
>> (for example someone starting a large download or streaming a HD movie
>> elsewhere) cause problems?
>>
>> Or am I better recording to local drives and using some sort of cron job
>> to move stuff to the NAS periodically?
>>
>> Or (thinking on the fly) should I abandon the 4 stand alone drives and set
>> them up in a RAID array locally?
>>
>> Any advice gratefully received.
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>
>
>I've previously recorded to my syncology NAS, and just recently last Friday
>moved back to using it (I moved away from it not for performance reasons,
>but space reasons. I moved back after I upgraded my NAS drives and moved my
>backend to a Raspberry Pi 2). I share the folder off my NAS via NFS and
>have set MythTV to keep 100GB free space (so I can move files to the NAS
>without worrying about free space).
>
>I've not seen any performance issues recording to the NAS. I've got a HD
>Homerun Prime.

I would recommend doing some performance testing on your NAS, then
calculating the Ethernet traffic also before using it for recording.
There are plenty of NAS boxes out there that perform quite badly, and
I have seen performance issues with recording directly to hard drives
when I only had two, so I would be very careful of using something
slower than hard drives.  Generally, a home made NAS box using an old
PC will perform better than a commercial one intended for the home
market - NAS boxes often have quite cheap small CPUs and have lots of
performance bottlenecks, and sometimes pretty bad software.  An old PC
tends to have a CPU and other hardware that matches its drives
performance capabilities rather better than a cheap NAS does.  The
downsides of using an old PC as a NAS are higher 24/7 power use (older
PCS use more power than newer ones), and maybe fan noise.

A good way to do a real life test would be to set up a special
recording group pointing to the NAS drive(s) and then just create some
one off recording rules set to record to that storage group.  See how
many recordings at once can be done safely, and try some other use of
the NAS at the same time.  Make sure to try starting a number of
recordings at exactly the same time, as the workload of a filesystem
can be substantially higher on file creation (or deletion), with the
heads have to move to the various parts of the drive where it keeps
directory and file information, as well as to the actual recording
files themselves.  And remember that HD recordings use lots more data
than SD ones, often four times as much, so they generate more disk
activity and more Ethernet traffic.

A NAS should be fine for moving recordings to after they finish
recording.  Just set up a separate storage group for the NAS drive(s).
MythTV will be able to play back files moved to that storage group,
but will only record to the Default storage group unless you tell it
to use another storage group in the recording rule.  Then a job run
automatically from cron or maybe at the end of a recording can move
files off the recording drive(s) to the NAS.  The only gotcha I can
see is if someone tries to play a file that is currently being moved
or the script tries to move a file that is being played or recorded,
so a script that ran in the middle of the night might be a good idea,
if your household is free of night owls.  Once the script has checked
that the file is not a current recording or playback file, a good
safeguard would be to have it rename the file it is currently moving,
so MythTV can not find it.  Then once it has completed the move to the
NAS drive, rename it back again.  Then there would only be a very
short window of opportunity for a clash for use of the file.  Once it
is renamed, it will show up in mythfrontend greyed out with an X icon
(or whatever your theme does for missing files).  If a file is shown
like that, you normally need to page up and page down or something
like that to get mythfrontend to refresh its status for the file so it
can be played.