[mythtv-users] Stuttering on some mpg files (PrebufferEnoughFrames)

[Stuart Morgan]

On Monday 23 Dec 2013 13:05:26 Ian Evans wrote:
> > yep, it's the USB drive. Don't know why it's giving me speeds so slow:
> > 
> > sudo hdparm -tT /dev/sdc1
> > 
> > /dev/sdc1:
> >  Timing cached reads:     2 MB in  2.05 seconds = 999.51 kB/sec
> >  Timing buffered disk reads:   4 MB in  4.10 seconds = 999.83 kB/sec
> 
> rebooted and got this for the same drive:
> 
> Timing cached reads:   3578 MB in  2.00 seconds = 1789.24 MB/sec
>  Timing buffered disk reads:  64 MB in  3.00 seconds =  21.30 MB/sec

Sounds like it's falling back to UDMA 0 (or worse) sometime after boot, the 
kernel falls back through different standards from fastest to slowest when it 
starts having trouble reading/writing to the drive at a higher speed. I've 
never seen a case where it falls back to reads at 1MB/sec though, that would 
suggest that either the driver is severely broken, or the drive is and the 
kernel is consistently finding that the drive is erroring out at higher speeds 
(UDMA 1-6, Sata 1-3).

This can happen particularly under heavy load. Once that happens it won't go 
back to full speed until a reboot. Keep an eye on syslog/dmesg and the 
appropriate sys node for that drive:
cat /sys/class/ata_link/link1/sata_spd
-- 
Stuart Morgan
MythTV