I've shuffled locations of my filesystem partitions; /myth/tv is now on a dedicated 80GB drive. However, since I've done this, I've seen that video playback from my recordings has a lot of audio and video quality issues- audio pops or skips, video has lots of artifacts or choppiness. The issues are also repeateable, so I'm assuming it occurs when the data is written, not read.

I've already made sure that DMA is enabled on the drive, so I'm wondering if I need to tune the filesystem on this new partion. My old /myth/tv parition had very few inodes, and I think I'd read about needing to tune ext3 for mythtv. I've googled quite a bit; can anyone point me in the right direction?

Something is wrong. The filesystem isn't really strained by playing back video data. You must have some other problem. If DMA is set properly, then there must be some other reason for the poor performance. Maybe some toxic IRQ sharing or just a failing hard drive.

For example, I can save two HDTV streams while playing back a third and the hard disk isn't even breathing hard.

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Having just done the math again recently I can tell you off the top of my head that, if DMA is working right, you should only be using maybe 1/20th of the disks bandwidth. Try this on your disks:

The lowest number I get is over 50Mb/sec.

/dev/hdc:
Timing cached reads: 1176 MB in 2.00 seconds = 586.92 MB/sec
Timing buffered disk reads: 72 MB in 3.04 seconds = 23.68 MB/sec
/dev/hda:
Timing cached reads: 1232 MB in 2.05 seconds = 601.07 MB/sec
Timing buffered disk reads: 90 MB in 3.01 seconds = 29.89 MB/sec

The /myth/tv partition is on /dev/hdc1.

I tried rebuilding the filesystem with mke2fs -j -O sparse_super -m0 -i 8000000 /dev/hdc1, but I still see video corruption.

I'm reading and writing data at the same time right now, and according to iostat, my disk bandwith is still about 55% idle.

Any other suggestions?

Just out of curiousity can you try this:

and maybe this:

What does the rest of the system contain? Despite the fact that my drives report twice the speed on buffered disk reads, I suspect the HD isn't your problem unless the DMA has an issueon your MoBo.

for the record, my motherboard is an ASUS A7NX8-E Deluxe.

/dev/hda:
multcount = 16 (on)
IO_support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 65535/16/63, sectors = 80026361856, start = 0

/dev/hdc:
multcount = 16 (on)
IO_support = 1 (32-bit)
unmaskirq = 1 (on)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 65535/16/63, sectors = 80026361856, start = 0

/dev/hda:

Model=WDC WD800JB-00CRA1, FwRev=17.07W17
Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
RawCHS=16383/16/63, TrkSize=57600, SectSize=600, ECCbytes=40
BuffType=DualPortCache, BuffSize=8192kB, MaxMultSect=16, MultSect=16
CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=156301488
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
AdvancedPM=no WriteCache=enabled
Drive conforms to: device does not report version:

* signifies the current active mode


/dev/hdc:

Model=WDC WD800JB-00CRA1, FwRev=17.07W17
Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
RawCHS=16383/16/63, TrkSize=57600, SectSize=600, ECCbytes=40
BuffType=DualPortCache, BuffSize=8192kB, MaxMultSect=16, MultSect=16
CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=156301488
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
AdvancedPM=no WriteCache=enabled
Drive conforms to: device does not report version:

* signifies the current active mode

Bizarroland, my hda is an earlier model of the same WD drive: Model=WDC WD800JB-00FMA0, FwRev=13.03G13 but it's timings are much faster...

Still I don't think that's the problem, and your MoBo's Nforce2 Ultra 400 / MCP-T chipset should be plenty fast.

Do you boot with "noapic noioapic" to avoid serious clock drift?

Do you have a lot of devices in the box or a long filter chain for playback? What are you using for a capture card? What's the rest of your hardware stack?

I just added noapic noioapc to LILO and rebooted, but I see the same issue. My filter chain is whatever is stock with knoppmyth, I haven't modified it. I have 2 PVR-250's in the box, and those are the only expansion cards. Full rundown:

NVidia GForce 5200MX AGP card
1GB Mushkin DDR 2100 RAM
the 2x 80GB drives
NEC DVD+-RW
AMD Athlon XP 2200+
IRMan serial IR adapter

That's all; was gonna add a WiFi card and swap the 80GB drives for a pair of SATA disks, but I don't have the money for the disks, and the WiFi card is being used in another box right now.

The video and audio jerking happens whether I'm watching live TV, or just playing back the files. It looks like the kerking is actually being written into the video files themselves; when I transcode the files into, say, XVID and play them on another PC, I see and hear the exact same artifacts. Maybe its my tuner cards that need work, not my filesystem?

Hmmm... What is your CPU core? Better yet was does this show for you?
I seem to remember something about certain chipsets or CPUs doing better with less than 1Gb because of caching issues but it's pretty fuzzy and I'd have to hunt it down...

Oh, and I'd guess the glitch is downstream from the capture card. What does "top" show if you run it during a recording?

that last reply was while I was watching live TV. here's top while recording 2 shows simultaneously: