[mythtv-users] Hard Drive Performance

Brian Wood beww at beww.org
Thu Mar 30 16:15:15 UTC 2006



On Mar 30, 2006, at 8:53 AM, Ryan Steffes wrote:

> I've been using my machine for a while now, with only minor  
> problems, so I've been pretty much leaving it alone (Running a cvs  
> from Julyish).  Lately though, some of the little things have been  
> annoying me more, so I thought I'd ask to see if anyone had  
> suggestions.  The primary problems appears to be my hard drives  
> can't keep up.  I've got 2 IDE drives as hda and hdc, and a CD  
> burner as hdd.  When I say say can't keep up, I mean that there are  
> noticable pauses in playback when recording, especially of  
> commercial flagging or something else is going on in the  
> background.  Sometimes then something is being recorded during one  
> of these disk usage times the audio on the recorded program  
> "glitches", and when we go to watch that recording, there will be a  
> glitch in the video, and all the audio after that glitch has this  
> weird reverb effect.
>
> The recordings are off a single PVR150 (ivtv version 0.3.8 ).
>
> [root at mythtv mythtv]# hdparm -tT /dev/hdc
>
> /dev/hdc:
>  Timing cached reads:   1392 MB in  2.01 seconds = 692.30 MB/sec
>  Timing buffered disk reads:  188 MB in  3.00 seconds =  62.63 MB/sec
> [root at mythtv mythtv]# hdparm -tT /dev/hda
>
> /dev/hda:
>  Timing cached reads:   1368 MB in  2.00 seconds = 683.76 MB/sec
>  Timing buffered disk reads:  124 MB in  3.02 seconds =  41.12 MB/sec


Your buffered reads look more or less normal, but your cached reads  
are less than half of what they should be. I get over 1900 MB/sec.  
for cached reads.

Are you sure DMA is enabled for your drives ?? Was the system doing  
anything else when you ran the tests?

You never want to put a hard drive on the same IDE bus as an optical  
drive, it will slow the HDD down to the (probably 33) speed of the  
latter. You should put both of your hard drives on the primary IDE  
channel. This, however, does not explain the slow speed of your /dev/ 
hda drive, but it would explain problems with /dev/hdc.

Make sure you are using a proper 80-conductor cable for your hard  
drives as well, you need to be running in UDMA mode to get top  
performance (assuming your Motherboard has a modern IDE interface,  
without that you're pretty much dead in the water).

> [root at mythtv mythtv]# mythbackend --version
> 0.19.20050712-1
> Options compiled in:
>  linux release using_v4l using_oss using_alsa using_ivtv  
> using_dbox2 using_lirc using_joystick_menu using_x11 using_xv  
> using_dvdnav using_xrandr using_frontend using_backend
>
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/hdc1             282M  146M  122M  55% /
> /dev/mapper/vg-video  395G  343G   53G  87% /home
> /dev/mapper/vg-music   20G  7.3G   13G  37% /mnt/music
> /dev/hdc5             471M  8.1M  439M   2% /tmp
> /dev/hdc6             2.8G  1.5G  1.2G  58% /usr
> /dev/hdc2             471M  232M  215M  52% /var
>
>
> Anyone had any similiar problems, or suggestions?  I, foolishly,  
> didn't put my drives into a RAID format, and I think they are too  
> full to consider trying to adjust the lvm to use striping now.   
> Does anyone have any suggestions for what might improve  
> performance, or know what might be causing that reverb?

RAID should not be necessary to get satisfactory performance with SD  
video from a PVR card. It can't hurt, but it's not needed, and RAID-0  
does theoretically double the chances of drive failure crashing your  
filesystem.


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