Alternate paths and load balancing

[Dave Wherry]

Does Tru64 have alternate I/O paths?
If so, does it do load balancing on the paths?
If not, is there a third party or add on application that would do it?

[Stephen Carpenter · Accepted solution]

A multipathing SCSI subsystem was introduced in Tru64 UNIX V5.0. All valid paths to a device are automatically used and path failures are handled transparently to the user. The load balancing uses a round robin with queue depth weighting algorithm.

[Dave Wherry]

Stephen,
After posting the question we found a note mentioning multi-path. Just a mention though. Thanks for the explaination.

Dave

[Alexey Borchev]

Multi-Path load balancing & failover operates with Fiber channel storage as well.

It's quite a fun to see how Trunix sees 'SCSI bus' inside external storage and shows disks from that storage on that bus!

[Orrin]

Hi,

This gets really interesting in a Clustered environment.... especially if you set up the CI in as a LAG rather than a Netrain pair..

Regards,
Orrin.

[Hein van den Heuvel]

In addition to the queue based load balancing pointed out in the first reply, if is important to know that Tru64 will as the first rule to select an alternate path uses the 'nearness' of the interface in a numa box.

So a process on a given RAD in a GS320 (wildfire) or GS1280 (Marvel) will use the HBA on that RAD if there is one, or on the nearest neighbour RAD if there was none.

Now on a GS320, once you have to go outside the local rad it really does not matter much which HBA is used, but the 'nearest' neighbour still generates a more fair distribution.

hth,
Hein.