ISC 2.2 Hangs on disk I/O

[David Rector]

In <24113 at hydra.gatech.EDU> doug at pravda (Doug MacKenzie) writes:

>I have a Modular Circuit Technology's 25MHz cache 386 system.
>I have a Western Digital WD1006V-SR2 RLL controller with a Segate
>ST-277-1 65MB RLL Harddisk with DOS in the first ~8Meg partion and
>ISC 2.2 UNIX in the rest.  /etc/partions contains an accurate map
>of the bad sectors in the unix partion.

>The problem:
>  Some times during disk I/O, the disk light will just stay on solid
>  and the system is locked up.  I can not get any response other than
>  turning the stupid thing off.

>  It happens sometimes during boot up when it is scanning the disk.
>  It happens sometimes during large GREP's.
>  It just seems to happen!!!
>  This is not a panic.  It is just hung.

>Does anyone have any ideas?

>		Doug MacKenzie
>		doug at cc.gatech.edu

Ah, another sufferer.  The disease seems to be incurable, but you won't
notice it after a while.

No one has firmly diagnosed this problem with the otherwise admirable
WD1006, but the behavior suggests that an error condition is not being
correctly handled by the ISC driver.  Conjecture: controller is asked
to read a flakey sector; CRC comes up bad too many times and controller
gives up; driver doesn't have a time-out and never sees error message
or resets the controller; system hangs.

The cure is time.  ISC relocates sectors which show frequent bad
crc's.  After a few weeks the problem will occur only rarely.
Experiments suggest that the process might be speeded by writing and
running a short program that will read all of the disk sectors
(whether in a file or not).

Boot sectors, which cannot be relocated, might cause more permanent
problems.  Change the boot cylinder.

The supurb performance of the WD1006 makes up for this minor inconvenience.



-- 
David L. Rector				drector at orion.oac.uci.edu
Dept. of Math.				U. C. Irvine, Irvine CA 92717