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

[Mark Perkins]

> On 2 Jun 2015, at 7:51 am, "Jason But" <jbut at swin.edu.au> wrote:
> 
>> On 06/02/15 02:51, Gary Buhrmaster wrote:
>>> On Mon, Jun 1, 2015 at 3:08 PM, Tom Hayward <esarfl at gmail.com> wrote:
>>> .... If 8 programs are
>>> recording, it will need to seek to 8 different disk positions per
>>> second
>> Depending on the specific file system type, it can actually
>> be more than that, since the metadata also needs to be
>> updated, which may require other metadata to be updated.....
>> Whether those are forced to be synchronous (or can be
>> bundled to mitigate against the seek penalty) or not will
>> also depend on the file system type and settings such as
>> barriers.  Many of the consumer NAS devices do not let
>> one have full control over some of these capabilities.
>> 
>> And there are many possible configurations of most NAS
>> devices (i.e. raid topologies), some of which may also
>> require many reads to satisfy the write.
>> 
>> And while recording is not usually disk intensive, your
>> particular environment will vary.  As per the previous poster,
>> test, test, test, and then test (with at least twice the load
>> you expect to ever encounter, and ideally a much larger
>> multiplier since I/O is not constant, but bursty).  Once
>> you know the maximum you can run with, you will be
>> able to make a more informed decision regarding how
>> close to the maximum you wish to live.
>> _______________________________________________
> 
> Therealways seems to be people querying recording rates, yet I have never seen problems. My current install has Myth running on the same physical box as my 6-disk RAID-5 array and I have never seen any problems with up to 7 concurrent recordings, two concurrent playbacks, while the same box is also my home network gateway, file server, DNS server, print server, everything else server. While the computer is an i5 and not a cheap NAS, the disks are surely not going to be a problem...
> 
> Jason
> 
> 
> -- 
> 
> ----------

I understood the query to relate to network I/O. Having your disk on the same machine as the backend will result in completely different writing and buffering characteristics compared with an NFS mount which, for example may not have any buffering and may just drop packets during transient congestion spikes. As I understand it at least.

In your situation I would expect substantial stuttering of the playback before the loss of any recording information. Recording to a NFS mount might result in recording loss before playback stuttering is even visible.