how to limit SCSI TCQ depth in FreeBSD? (SUMMARY)

[Frantisek Rysanek]

Dear gentlemen,

many thanks for everyone's responses - all of them helpful, 
all of them to the point.

Let me reiterate a short summary of the responses:

1) "it's the firmware that is broken, try to get an update"
-- exactly what I've tried in the first place. In the 
meantime, I've obtained a newer FW version from the 
manufacturer, and I'll try to flash it today. 

I did not disclose the name of the device deliberately, before 
I give an opportunity to the manufacturer's tech support.

2) "use `camcontrol tags da0 -N <depth>`"
-- works like a charm. This is what I was looking for.

Someone else has pointed out that this should be hooked
up early into the rc scripts, before fsck starts up.
That is, if the volume is mounted and auto-fsck'ed
on startup - see /etc/fstab.

3) "try adding an entry to the xpt_quirk_table in 
sys/cam/cam_xpt.c for your disk"
-- a good idea, didn't have the time to test it yet,
I'm pretty sure it would work, though. If the firmware
update doesn't help, this could be a proper long-term 
workaround.

4) "try this patch to aic79xx_osm.c"
http://lists.freebsd.org/pipermail/freebsd-scsi/2003-
August/000443.html
-- I'm pretty sure this would work too. Didn't have
the time to try it out, though. IMHO this solution is
not as formally clean as adding an entry into the quirks 
table.


To sum up, I have obtained several ways to work around
my problem :)
The one involving camcontrol is good enough for me.
I understand that the OS-based workarounds won't help me
to install FreeBSD on the faulty drive from the original 
installation media, but I guess I could manage that somehow 
"out of band" - and it's not my goal in the first place,
the flawed drive is not my boot drive. With respect to
booting off the culprit drive, it's my drive that is flawed, 
not FreeBSD.
While I was testing the drive with Bonnie in Linux and 
FreeBSD, I got familiar with some aspects of the FreeBSD 
SCSI/CAM (compared to Linux) and I have to say I am impressed 
by FreeBSD's performance.

Thanks for your care :-)

Frank Rysanek