[mythtv-users] recording drive bottle neck suggestions..

[James Crow]

sonofzev at iinet.net.au wrote:
> Hi All 
>
> On Sunday night I ended up having a bottle neck as it was the first time I ever
> had 5 recordings going at one (1 HD 4 SD)... the system choked and I couldn't
> watch as the recordings were going (although it appears the recordings ended up
> fine).. The system couldn't seem to playback live TV or even a recording while it
> was being recorded without major stuttering (F1 race so it was important!!)
>
> The cpu seemed fine so I am assuming this is a bottle neck but it's only dual
> core.. do I need more cores for this type of operation?
>
> Ultimately I would like to be able to record 3 HD streams and 3 SD streams
> simultaneously and playback 1 of those streams.. .. but that's just a wish.. not
> a necessity.. 
>
> My MBE recording drive is on an LVM partition on a 4-disk RAID 5 configuration...
> With 300 GB set aside for recording... Itis on XFS with tuning for the RAID
> configuration (large extensts and sunit and swidth)
>
> I am about to migrate to a bigger case and will have enough room for at least 2
> more drives.
>
> Here are the options I see.
>
> 1. Add 2 more drives to the RAID 5 partition. This is my first preference as I am
> hoping this will add enough bandwidth to record 5 shows.
>
> 2. Create a new RAID 0 for recording only removing the original 300GB partition
> to utilise for extra space for transcoded videos. (will this be enough?)
>
> 3. Add 2 disks not in RAID and include them in the list of recording drives
> deleting the original partition
>
> 4. Add 2 disks not in RAID and include them in the list of recording drives
> keeping the original partition
>
>
> I'd love your opinions on these or other potential options (that don't involve
> dismantling the existing RAID)
>
>
> Also, is XFS still worthwhile, or should I consider something like NILFS, btrfs
> or ext4? 
>
>
> I know that the simple answer is to restrict my tuners to record one channel at a
> time but I have found recently that the multiple recordings per instance is good
> especially with overlapping programs, now that it seems in Australia almost no
> channel runs to schedule anymore.. 
>
> cheers
>
> ALlan 
>   
You did not mention what kind of recorders these are, but if your SD 
recorders are framegrabbers you may be hitting a PCI bus issue rather 
than a hard drive issue. If they are DVB or hardware encoders than this 
should not be a problem.

The suggestion of another poster to add spindles outside of a RAID setup 
is good as well.

My system has three drives ( 1TB, 2x 500GB all XFS) for recordings and 
when I had all encoders connected I could have three HD and two SD 
recordings with three recordings being comm flagged while watching two 
recordings. (3x QAM, 2x PVR mpeg2) Three spindles was plenty to handle 
that load.

Another issue that might be a problem is comm flagging. My Athlon x2 
2.6GHz machines can comm flag SD material faster than live TV. This 
requires a read of the recording and puts more load on the disk system.

Cheers,
James