Disk Mirroring (was Re: Altos 5000)

[Brandon S. Allbery KB8JRR/KT]

As quoted from <truesdel.652083402 at sun418> by truesdel at sun418.nas.nasa.gov (David A. Truesdell):
+---------------
| dtynan at altos86.Altos.COM (Dermot Tynan) writes:
| >In article <1990Aug27.183821.13518 at ico.isc.com>, rcd at ico.isc.com (Dick Dunn) writes:
| >> I've seen as many motherboard and controller
| >> failures as disk failures.  I don't pretend my experience is typical, but
| >> suppose that it might be.  The disks are not the only failure points in the
| >> system.
| 
| >I suggest that you have some serious design flaws here.
| 
| Another design flaw would be to use a single controller to run both disks.
| Separate controllers running, running separate disks, could allow the system
| to continue running in spite of the failure of a controller or a disk.  If you
| get the software right, you would only have to come down long enough to replace
| a controller.  (If you get the hardware right, wouldn't have to do that!)
+---------------

Worst case uses the standard controller; one disk goes, the controller
switches to the other disk.  No down-time.  If the controller goes, you're
screwed.

But if you need disk mirroring that badly, you are using one or two HPFP
boards as well as the standard controller.  A controller goes, the mirror disk
on another controller takes over.  No downtime.  And since disk striping and
disk mirroring are the same mechanism in recent Altos OS'es (including the
current OS for the Series 1000), you can also configure for RAID.  And since
all three controllers are capable of independent operation, you lose very
little time doing the mirroring.

++Brandon
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