Re: Redundant fiber tape.

Got this reply back from IBM:
<snip>
Hello Rob,

I got to thinking about what EMC told you after we hung up. This might be
a terminology issue.

What is new for IBMi is 'multipath'. This is the ability to assign 2 paths
for a single tape device (tap01 for example) to a server (using either
multiple adapters or multiple ports on the same adapter to the device). If
one path fails, the operating system will automatically activate the other
path and attempt to continue the operation. IBMi disk has had this
capability for quite some time.
What EMC might be referring to is 'multiple path', splitting multiple tape
resources among multiple adapters or ports on an adapter (tap01 and tap02
attached to one adapter, tap03 and tap04 attached to another adapter for
example). This spreads the throughput across 2 adapters and allows the use
of all 4 tape drives simultaneously. However if, one of the paths fails,
the drives attached to that path will fail are cannot be used until the
problem is resolved. There is no fail over in that configuration. IBMi has
worked this way with tape for decades. It is nothing new. But with the
introduction of virtual tape, is now used much more extensively.
</snip>

Now I have to:
- figure out which path I want to take: additional redundancy or
'possible' faster throughput.
- Whether or not the Data Domain device even uses this new multipath

Apparently these devices are selling like hotcakes and they're really
busy. The guy I'm working with is so busy.


Rob Berendt