At 10:42 Uhr 30.08.1996, John F. Woods wrote:
>> What makes you think it's failing??  This disk is less than 6 months old
>
[...]
>
>(*) I once had a Maxtor 7245 disk which worked fine under UNIX for 6 months,
>but when plugged into a Mac would fail the nightly DiskExpress verify, with
>DiskExpress claiming that it successfully read *different data* on subsequent
>reads.  I wrote a UNIX utility to simply read every sector of the disk three
>times in a row, and sure enough, once in a while the disk would return data
>from a different sector.  APS Power Tools failed to discover this problem;
>they likely read the entire track at once (multiple times), and this turned out
>to be a caching bug.  Just by chance, my employer at the time was having
>regular visits from a Maxtor field engineer at the time;  I mentioned the
>problem to him, he said "nooo, it couldn't be doing that", and hooked it up
>to his official Maxtor test rig.  I swear there is still a dent in the floor
>where his jaw hit it...  He called up the engineering department, and they
>said they hadn't seen THIS bug, but there had been a vaguely similar caching
>bug which was fixed during the product lifecycle, and Fedexed out a new ROM.
>The field engineer said that if the ROM didn't fix it, I could return the
>drive to Maxtor for a replacement thanks to their "No Quibbles" guarantee,
>but the ROM did cure the problem.  (It turns out that at the time, the
>7245 drive wasn't being manufactured any more, but they were still shipping
>them -- 7345 (245MB capacity versus 345MB capacity) drives with the extra
>space disabled in firmware; if I went that route, the FE said he knew what
>microcode variables to tweak to uncover the extra space, but again, the ROM
>fixed it and the extra space wasn't worth the hassle.)


This rings a bell for me.

I've seen media errors twice on my MO, each time after a violent disk
driver related crash. Both times I tar'ed the data on the MO (NetBSD
-current kernel & userland sources, some 130 MB altogether); tar complained
about read errors but continued to pack the data, and the next sup run
restored what was lost.

Now when I reformatted the media it was found fine, and I never had any
problems after...

I agree that 'in principle' it is impossible for an OS to induce media
errors. But then, I had the write back cache of the drive enabled -- as
have most hard disks that are sold now -- and if the caching software is
not entirely waterproof then MacBSD's SCSI driver crashes may well find a
weak spot in it.

You don't see this much with MacOS because disk drivers are a little more
stable here. :)



	hauke

---
"It's never straight up and down"     (DEVO)