drive loses dma under load

[Jason Pepas <j.pepas@mail.utexas.edu>]

hello,

when under heavy load, my hard drive appears to lose DMA.

hdb: timeout waiting for DMA
ide_dmaproc: chipset supported ide_dma_timeout func only: 14
hda: status error: status=0xd0 { Busy }
hda: DMA disabled
hda: drive not ready for command
ide0: reset: success

no data loss or anything, I just have to run hdparm again to put it back into 
dma mode.

Uniform Multi-Platform E-IDE driver Revision: 6.31
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
SIS5513: IDE controller on PCI bus 00 dev 15
SIS5513: chipset revision 208
SIS5513: not 100% native mode: will probe irqs later
SiS735
    ide0: BM-DMA at 0xff00-0xff07, BIOS settings: hda:DMA, hdb:DMA
    ide1: BM-DMA at 0xff08-0xff0f, BIOS settings: hdc:DMA, hdd:DMA
hda: SAMSUNG SP8004H, ATA DISK drive
hdb: MAXTOR 6L040J2, ATA DISK drive

anyone else experience this?  any idea why this is happening?

by heavy load I mean making a tar.gz backup of my hard drive, which results in 
a roughly 12GB file.

thanks,
jason pepas