Slow PATA drive performance? Try this.

A few weeks ago I built an extra OMV box from some old parts, just for 0.5 testing, because I still use 0.4 with openvpn. Parts used: Asus P4P800DLX, P4 3ghz, 3 gig, four 200 gigs PATA/133 harddisks for storage (Greyhole) and one PATA/100 40 gig harddisk for the system. Everything installed perfectly and OMV was up and running in no time. But I noticed a slow drive performance, copying a file maxed out at 29 mb/s... Too slow imo, so digging into the logfiles, I found out that my drives were operating at ATA/33, strange...

So, Putty login and run:

dmesg | grep -i ata.*dma

Well, all the drives were running at ata33... But I saw also the following line:

limited to UDMA/33 due to 40-wire cable

Wait whut??? 40 wire cable??? Hmmm, no way, I used 80-wire cables. Okay, good old Google. Phew, I'm not the only one with that problem, but a simple answer was hard to find. After a long read and many tries I found the simple and working solution. Just add "libata.force=80c" to Grub after the "GRUB_CMDLINE_LINUX_DEFAULT" line, like this:

GRUB_CMDLINE_LINUX_DEFAULT="libata.force=80c quiet"

Update Grub, reboot, and problem solved. All my drives are now running at the right speed, and the copy speed is around 50mb/s now.

Maybe this could be helpful for people with an old PATA based OMV box, because I couldn't find a topic about this problem.