Auto trespass

[Lakshmi Nagarajan]

Can someone tell me why 'auto trespass' needs to be disabled on an FC30, when used in a campus cluster environment with MirrorDisk/UX?

[Bill McNAMARA_1]

it's a long story but boils down to the fact that:

if auto tresspass is off, you cannot access any luns through the non default owner SP (ie you cannot access the lun through an SP that did not create the Lun)

Accessing a LUN via a non default owner SP will result in a major perf decrease - that is once AutoTresspass is on.... but at least it works. (ie there is failover)

This can lead to problems: If you decide to access a lun all the time trhourgh the non default owner, you get crappy perf until the thing fails...

Windows cannot switch over just like that right, so AutoTresspass must be off here. In a non autotresspass environment, there are SPOFs - the controllers (the SPs as we say)

I suggest looking at some of my 'top answers' if you need more info..

Later,
Bill

[Lakshmi Nagarajan]

Bill: Thank you. But I still don't see the reason for turning off 'auto trespass' in a cluster environment. In fact, by doing so you only have one path to the local disk. Isn't that an SPOF?

[Bill McNAMARA_1]

With SG, yes it is a spof.. however, if you are mirroring an entire lun (4 copies really) it doesn't matter if it's on or off.

If it is on, you will get 4 device files for the same data: 1 for the lun through SPA, 1 for the lun through SPB, and 1 for each mirror through each SP.

When auto tresspass is off, there are only 2 device files, 1 for the lun through the owning SP, and one for the mirror through the owning SP.

It kinda makes the management easier.

If you switch off mirroring, you will want to switch on auto tresspass, but then, your device files will change and your vg will need to be modified. I'd recommend turning it on.

Later,
Bill