[mythtv-users] stutter while recording two programs at once

[Brad DerManouelian]

On Aug 25, 2006, at 1:58 PM, Drew Bernat wrote:

> On Aug 25, 2006, at 3:38 PM, Brad DerManouelian wrote:
>
>> I've got a PVR-350 and an HD-5500 card in the box which is also my
>> frontend. I'm getting weird stuttering when recording on both tuners
>> at the same time. The HD stream looks perfect but the stream from the
>> PVR-350 will show a single frame from about a second before the
>> current position. It happens intermittently but often enough to be
>> REALLY annoying. I've found that it's in the recording this way since
>> the rogue frames happen at the same place when I play back every
>> time. I have a feeling it MIGHT only be happening when watching a
>> program and recording two others at the same time. I had anticipated
>> 3GB/sec on the SATAII drive would be enough bandwidth to watch 1,
>> record 2. Is this not the case? Is there a good way to test?
>
> You can test the throughput of your drive with the following command:
>
> hdparm -T -t /dev/sda
>
>   -- assuming that this is the first SATA drive. You won't get 3 GB/ 
> Sec at a constant rate, because the drive isn't that fast. However,  
> it _should_ be fast enough.
>
> In any case, that will tell you disk throughput. For reference, I  
> get 2GB/sec for cached reads and 73 MB/Sec for buffered disk reads.
>
> Drew

[mythtv at mythtv ~]$ sudo /sbin/hdparm -T -t /dev/sda
Password:

/dev/sda:
Timing cached reads:   1856 MB in  2.00 seconds = 927.81 MB/sec
Timing buffered disk reads:  172 MB in  3.01 seconds =  57.12 MB/sec
[mythtv at mythtv ~]$ sudo /sbin/hdparm -T -t /dev/sdb

/dev/sdb:
Timing cached reads:   1844 MB in  2.00 seconds = 921.44 MB/sec
Timing buffered disk reads:  176 MB in  3.03 seconds =  58.06 MB/sec


These numbers seem acceptable to me.