[mythtv-users] Newbie

[Gavin Whitehead]

On 02/12/2011 22:54, Simon Hobson wrote:
> Eric Sharkey wrote:
>
>>   >>  Don't raid or stripe your recording disks together, you'll get better
>>>>   performance with individual disks.
>>>   I'm in the process of building a MythTV combined FE/BE and I had thought
>>>   to put in 2 x 2TB SATA disks for the recordings and video/music
>>>   library.  I was going to use RAID1 (mirror) so that a single disk
>>>   failure didn't mean I loose all my recordings and ripped videos/music.
>>>
>>>   But you seem to be advising against this approach.  How do you protect
>>>   against data lose if not via RAID?
>> He said performance, not reliability.
>>
>> Your choices are either backup or prayer.  For mythTV recordings, I
>> just keep my fingers crossed.  I lost a recording drive once.  The
>> world didn't end.
> Exactly.
> Some people have suggested striping their disks into one virtual
> volume. This may be better for some tasks, but because of the way
> Myth works, it will be significantly inferior for Myth. As i said,
> the primary constraint for most people seems to be when handling
> multiple streams - and disk seeks are the killer there. If you stripe
> your disks, then you are guaranteed that all the active streams will
> be operating on both disks - and the slowest seek time will set the
> overall performance, effectively the performance of the array will
> never be higher than any of the disks.
>
> If you use the disks separately (Myth handles an arbitrary set of
> recording directories), then most of the time you will have the
> streams spread across the drives. By default, Myth will try and
> balance recording jobs across all the recording directories. Thus the
> throughput available to you will be much higher.
>
> Eg, if one drive could handle 3 streams, then 2 drives could handle
> 6, 3 drives could handle 9. Obviously it's not as simple as that as
> you could end up with (say) 6 streams split 2&  4 across 2 drives -
> but you'd be unlucky to have (say) 4 streams on one drive and none on
> the other.
>
> Also, if you have multiple drives, then you don't lose all your
> recordings if one dies.
>
> As to mirroring two drives. I suspect the throughput would be fairly
> close to the throughput available on the slowest drive.

Thanks for the insights.  I will reconsider my approach with the disks.
Perhaps an SSD for OS and SQL and then use the two large disks as 
separate recording/library stores.

Gavin