Thanks to:
Ram Rao, UNIX* Consultant, Indianapolis [alphaosf_at_ini.dec.com]
Lars Bro [lbr_at_dksin.dk]
alan_at_nabeth.cxo.dec.com
Bruce Hines [Bruce.Hines_at_mci.com]
I got a lot of good information and some pretty picutres of how to layout
the disks. An interesting piece of advise was not to worry about it too
much. The HSZ70's are fast enough that it shouldn't be a problem.
for the archive here's Alan's response, the other's pretty much followed the
same course:
----------------------------------------------------------------------------
------------------------------
Each device, storage set and logical unit will only be accessed by
one controller or the other. The logical units are the SCSI devices
that the host sees and are presented by which ever controller uses
that target ID. So if you define one striped mirror aray as being
unit D0 and the other as D200, you'll spread the I/O load (to the
extent it can be) between the two controllers.
Each has controller has six back-end SCSI busses for connecting
devices. In the BA370 cabinet the busses run vertically, four
devices per bus. Wanting only two logical units to be seen by
the host, your configuration options are fairly limited and there
is only much you can to spread the load among the six busses.
You can split two device mirrors between two busses each (a mirrored pair
indicated by <=>):
B B B B B B
u u u u u u
s s s s s s
1 2 3 4 5 6
+---+---+---+---+---+---+
| x | | | | | |
| x | | | | | |
| x | | | | | |
+---+---+---+---+---+---+
| x | x | x | x | x | x |
| x<=>x | x<=>x | x<=>x |
| x | x | x | x | x | x |
+---+---+---+---+---+---+
| x | x | x | x | x | x |
| x<=>x | x<=>x | x<=>x |
| x | x | x | x | x | x |
+---+---+---+---+---+---+
| x | x | x | x | x | x |
| x<=>x | x<=>x | x<=>x |
| x | x | x | x | x | x |
+---+---+---+---+---+---+
But then, to build two stripe sets, you'll have to have some of
the striped device on the same bus. You could build three
stripe sets that didn't reuse a bus within the stripe set,
but that may unbalance the load between the two controllers,
with one having two logical units and the other one. Mirroring
among disks also protects against a failure of the backend
SCSI bus.
Or, you could mirror on the same bus, but if the bus fails you lose
at least one mirrored device or perhaps two; many single failure
points.
If you only go with one spare, the two stripe sets will be
different sizes. If you three disks as spare, you can make
the stripe sets the same size. If you went with four stripe
sets and three spares you could logically balance the devices
among the two controllers, but the host load may not cooperate.
---------------------------------------------------------------
Daniel Monjar
Manager, Systems
Organon Teknika
Mailto:Daniel.Monjar_at_orgtek.com
Received on Mon Nov 16 1998 - 15:08:26 NZDT