ISC 3.2/harddisk & floppy problems

[Ed Hall]

In article <rcbarn.677172100 at rwc.urc.tue.nl> rcbarn at urc.tue.nl writes:
>marzusch at odiehh.hanse.de (Ralph-Diether Marzusch) writes:
>>2nd problem:
>>     If you connect two (!) hard disk drives to one (ore even two) `standard'
>>     AT type hard disk controller (i.e. MFM, RLL or ESDI drives) you may
>
>This statement is *very* inaccurate!!  see below.
>
>>     experience a `hanging' disk controller (making any further disk accesses
>>     impossible which possibly destroys one or more file systems) when both 
>>     disks are accessed concurrently 
>>
>>There seem to be no solutions to these problems, just some workarounds:
>
>This statement is even more inaccurate!!  see below.

It might be.  I've had infrequent but persistant lockup problems with
ISC and a WD1006SR2 and a *SINGLE* disk.

>That does it! Oh Connor, if you're reading this, please add this issue to the 
>FAQ list!!
>
>Here we go again:
>
>The second problem, the one with the HD controller locking up under ISC
>is known to occur in combination with Western Digital's WD1006Vsr2 RLL
>controller; it contains a bug which only occurs if 2 drives are
>attached to it and if the HD device driver has the 'overlapped-seeks' 
>feature enabled, like the one in ISC/ix has by default. It does not
>happen with ESDI.

Wrong, at least in my case and in the case of some other folks who
have written that they have the lockup problem.  THERE ARE TWO DIFFERENT
PROBLEMS WITH THE WD1006SR2 AND UNIX.  The second problem doesn't even
seem to be limited to ISC; there was a fellow running ESIX who posted
a complaint about it a few months back.  I exchanged messages with him
and verified that it had nothing to do with the overlapped-seek problem.

The overlapped-seek problem bites much faster, and tends to cause bad
data to be read and/or written to one or both disks.  The lockup
problem generally happens after hours of heavy use, especially when a
lot of expansion swaps are taking place. (Adding memory almost
completely cured my problem--from a few lockups a week to one every
few months).  The symptom is that the disk light comes on and stays on
(this is similar to what can happen with the overlapped-seek problem);
after a reset, damage to filesystems is generally limited to unflushed
buffers (which differs from the overlapped-seek problem, which frequently
trashes one or more filesystems).

The clincher is that the lockup problem can happen with just a single
disk.

As you state, there is a relatively simple fix for the overlapping
seek problem--simply disable overlapping seeks.  I wish that the
solution for the lockup problem were so simple.

		-Ed Hall
		edhall at rand.org