On Wed, Sep 26, 2007 at 05:15:08PM -0400, bob944 wrote:
> Perhaps anything can have a failure mode where it doesn't alert--but in
> a previous lifetime in hardware and some design, I saw only one
> undetected data transformation that did not crash or in some way cause
> obvious problems (intermittent gate in a mainframe adder that didn't
> affect any instructions used by the OS).  

There's a lot more data out there now (more chances for problems).
Disk firmware has become much more complex.

> I don't remember a disk that didn't maintain, compare and _use for error
> detection_, the cylinder, head and sector numbers in the format.  

Disks may (usually) do that, but they don't report it back to you so you
can verify, and they're not perfect.

One of the ZFS developers wrote about a disk firmware bug they
uncovered.  Every once in a while the disk would return the data not
from the requested block but from a block with some odd calculated
offset from that one.  Unless the array/controller/system is checking
the data, you'll never know until it hits something critical.

Netapp also talks about the stuff they had to add because of silently
dropped writes and corrupted reads.

Everything has an error rate.  

-- 
Darren Dunham                                           ddunham AT taos DOT com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >
_______________________________________________
Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu