p...@petelancashire.com (Pete Lancashire) writes:
> Showing my age ....
>
> I worked for Burroughs as an engineering technician.
>
> A customer with 360/65 instantaneous loss of power. I was there only for a
> couple hours to drop off some equipment. Later heard they lost a couple
> disk packs.
separate from power failures can precipitate disk drive failure.
IBM CKD dasd had power loss failure mode ... where there wasn't enough
power to maintain memory contents ... but there was enough power left
for the controller to complete a write operation ... problem was that
the channel had stopped transferring data ... so the controller
continued writting all zeros. The result was that after recovery, a
subsequent read would show no errors ... for the record that had write
operation ("correctly") complete with all zeros (this was especially
troublesome when things like VTOC record was being written)
FBA introduced that a physical record would not be written unless all
data was available to correctly complete a write. This philosophy
continued for RAID (write "failure" either completes correctly or
at least results in error indication for subsequent read).
During the 80s, there was lots of work trying to figure out how to
retrofit such a fix to CKD dasd ... or at least provide a way for system
to recognize an incorrect trailing zeros write.
--
virtualization experience starting Jan1968, online at home since Mar1970
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
