Promise PDC20267 ATA RAID, poor write performance

astesin at astesin at
Mon Sep 13 04:12:58 PDT 2004

Dear Frode,

> > Any ideas as of how to debug this?
> Sounds strange indeed, there is some performance degradation to be 
> expected from RAID1 (you have to write to both disks) but 
> nothing that ruins performance this badly. I cannot reproduce it no matter
what I 
> try, so I'm pretty sure the reason should be found outside 
> ATA. It could be because the two channels are competing for 
> the PCI bus and the arbitration of that fails so you get alot of PCI
retries, that is 
> outside ATA's reach to control..

Dealing with Intel mobos for about 10 years, I should mention that almost
100% of those strange problems are solved with BIOS upgrades, issued by
Intel pretty much silently. I suggest going to and to get
the very-very-latest BIOS for your board somewhere at "support and
download", put it into, make "Load default settings", reboot, than set
whatever settings you need (including "RAID enabled"), tell it to "reset
config settings", reboot into FreeBSD and try testing again. I'm almost sure
that RAID firmware will be also upgraded together with BIOS upgrade and you
have a good chance to win. With D865PERL motherboard BIOS upgrade to P19
helped to solve non-trivial ATA RAID problems for me last week.

Additionally, I'll be installing BETA4 onto the box with Intel S875WP1
w/Promise RAID this evening, RAID 1+0 configuration (4 Western Digital 7200
SATA drives, not Raptors), and I'll check it myself and see what happens.
Will inform you ASAP.


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