[Gllug] SCSI device ID to ACTL mapping?

[Ian Northeast]

I'm just starting to use multipathed SAN storage with Linux and this 
means that the sd? name to Adapter,channel,target,LUN mapping keeps 
changing. Whenever a new disk is zoned in its path on adapter 0 is 
detected before all the paths on adapter 1 so all the latter get moved 
down. What used to be sdg now becomes sdi for instance. The LVM takes 
care of it if you get it right, so it's just somewhat inconvenient ATM 
but I can see it causing major havoc when I have to transfer 
administration to India. Which I will have to, sometime, it's not optional:(

I'll be looking at using "scsidev" to assign permanant names to SCSI 
devices, but one thing which would be really useful would be a reliable 
way to map sd? names to A/C/T/Ls. I assumed that this would be easy 
enough, the kernel must know after all or the devices wouldn't work. But 
I can't find any easy way to get it to tell me "sdb is scsi0, channel 0, 
target 1, LUN 1" or such like, except in the messages the driver issues 
as it's loaded, which can't be relied upon to be available. Nothing in 
/proc seems to contain this information. Does anyone know how to find this?

I'm using SuSE Enterprise 8 which is a 2.4.21 kernel, albeit heavily 
modified by SuSE, so anything which only works in 2.6 won't work. We're 
about to put Lotus (IBM) Domino (Notes) on this platform and IBM say 
they want SLES8 not 9, so 2.6 isn't an option ATM.

I have to say that with respect to SCSI device naming Solaris with its 
klunky old "c0t2d0s1" type stuff or AIX with its persistent virtual 
names both seem preferable to the way Linux does it.

PS if anyone thinks installing Notes is a bad idea, most of our 
influential users wanted Outlook/Exchange. In this market it seems to be 
a case of "least worst".

Regards, Ian



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