[mythtv-users] Multiplexing vs multiple cards

[Michael T. Dean]

  On 11/04/2010 01:39 PM, Steven Adeff wrote:
> On Thu, Nov 4, 2010 at 1:28 PM, Gavin Hurlbut wrote:
>> On Thu, Nov 4, 2010 at 9:35 AM, Steven Adeff wrote:
>>> As others have said, the demand on your hard drives goes up with every
>>> additional stream being recorded. Ideally you would have one drive per
>>> possible stream in storage groups. For instance, I have two DVB cards
>>> and I have them set to multiplex up to three channels since where I'm
>>> at I have a few frequencies with 3 channels. I also have two cable
>>> boxes. I have six 500GB SATA drives set up using storage groups. I
>>> have yet to have any issues with my hard drives not being able to keep
>>> up with the simultaneous recordings, viewings and commflagging.
>> The demand on the drives obviously goes up with every stream, however,
>> I think people are maybe overinflating that demand.  Modern hard
>> drives can easily deal with 50-60 MB/s (even the slow ones).  This
>> translates to 400-480Mbit/s.  HD streams over the air, etc, use up to
>> about 36Mbit/s for the entire multiplex (Is my math right there,
>> Raymond?).  Hence, even with "slow" 5400RPM drives, you should have no
>> issues at all with the disks if you are being somewhat careful.
>> Granted, the seeking overhead kicks in, but even then, even the slow
>> drives should be able to easily deal with 7 or 8 *multiplexes*
>> recording at a time.  Not many of us even get close to that.
>>
>> Of course, you'd need to keep the mysql database on different drives,
>> etc.  But really, if you are using current drives, your drives
>> shouldn't be the bottleneck for quite some time.
>>
>> Am I missing something here?
> it's not just recording, but also playback. the more different files
> you are reading/writing the more the heads have to move around. I
> think you can expect to be able to record a few streams and play back
> a few without issue (as long as your database is on a different
> drive), but the more you ask the system to do the more your really
> going to want to spend the money to add another recording drive.

Yeah, I use > one file system per possible overlapping recording 
specifically for the minimization-of-file-system-fragmentation benefit 
provided.

Also, just to clarify the above, note that recording 3 shows from the 
same multiplex is still 3 recordings = 3 separate files on the file 
system(s)--it's not just one recording that contains the whole multiplex.

Mike