order of sd? drives and mdadm

[Yan Seiner <yan@seiner.com>]

I think I have a problem with device naming.

My machine consists of 2 identical SCSI drives, 6 identical SATA drives, 
and 1 USB drive.  All show up as sd? devices.

The problem is that on boot, occasionally the machine fails to boot, 
with mdadm complaining it can't
start /dev/md0 and / doesn't exist.

I suspect what is happening is that the scsi devices change from the 
time the system boots up and when the kernel assigns the device names, 
in effect pulling the rug out from under mdadm.

I suspect this because the device names change from boot to boot, and I 
have to retry booting numerous times before I get the right combination.

So... Two questions:

1.  Does this sound reasonable?

2.  If so, how can I write rules to make sd device names sticky?  I'm 
leery of just hacking away as if I really bugger things up I could make 
the machine unbootable.

Just from looking at things, it looks like I should be able to use

    KERNELS="2:0:2:0",  SUBSYSTEMS="scsi", NAME="sda"
    KERNELS="2:0:8:0",  SUBSYSTEMS="scsi", NAME="sdb"

and so on.  Does that sound right?  Where in the rules should I put this?

Thanks,

--Yan

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