Every 12-hrs -- "ad0: TIMEOUT - WRITE DMA"

[V.I.Victor]

For the last 4-days, our (otherwise OK) 5.4-RELEASE machine has been
reporting:

Feb 12 12:08:05 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2701279
Feb 13 00:08:51 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2701279
Feb 13 12:09:38 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2963331
Feb 14 00:10:24 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2705947
Feb 14 12:11:09 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2706335
Feb 15 00:12:02 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2832383
Feb 15 12:12:57 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=139839
Feb 16 00:13:50 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=131391
Feb 16 12:14:36 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=131391

The system was created Jan 08 and, prior to the above, the ad0: timeout had
only been reported twice:

Jan 25 11:43:34 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=17920255
Feb 6 11:59:42 : ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=2832383


Before to asking here, I did several searches for possible causes. I think
I've eliminated disk spin-down and bad-block-mapping -- just before the Feb
15, 12:12 period a 2-gig file was created; leaving the disk 'spinning' and
bad-blocks presumably bypassed.

Another found item said that some IBM drives recalibrate every 25-hours.
Interesting concept, but a different period and without previous history.

Lastly, several items referred to changing PREEMPTION but never seemed to reach
a final conclusion.

I also checked the cron log and found nothing running at the timeout times.


So -- can anyone help track this down?


Final note: the hardware is an old, resurrected Win98 machine running 24/7
and is used only for email processing. I installed it primarily as a proof
of concept, so it can be replaced if necessary.

Some specifics:

FreeBSD 5.4-RELEASE #0: Sun May 8 10:21:06 UTC 2005
CPU: AMD-K7(tm) Processor (598.84-MHz 686-class CPU)
Origin = "AuthenticAMD" Id = 0x612 Stepping = 2
Features=0x81f9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,MMX>
AMD Features=0xc0400000<AMIE,DSP,3DNow!>
real memory = 134152192 (127 MB)
avail memory = 121630720 (115 MB)
ACPI disabled by blacklist. Contact your BIOS vendor.
ad0: 14664MB <IBM-DJNA-351520/J56OA30K> [29795/16/63] at ata0-master UDMA66
acd0: CDROM <CREATIVE CD5233E/C2.05> at ata1-master PIO4

Thanks for any help!