UNIX for Dummies Questions & Answers

Hi all,
I've got a system here in which I have put a hard drive that was previously mirrored in a supposedly identical system. I am now attempting to boot from this drive alone but get these messages:
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ad4: 58644MB <Maxtor 6Y060L0> [119150/16/63] at ata2-master UDMA100
Mounting root from ufs:/dev/ar0a
no such device 'ar'
setrootbyname failed
ffs_mountroot: can't find rootvp
Root mount failed: 6
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From mountroot> I attempt to do this:
ufs: /dev/ad4a
and then I get:
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Mounting root from ufs:/dev/ad4a
swapon: /dev/ar0b: Device not configured
Automatic boot in progress...
Can't open /dev/ar0a: Device not configured
/dev/ar0a/: CAN'T CHECK FILE SYSTEM.
/dev/ar0a: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
Automatic file system check failed . . . help!
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I went from there into the default of /bin/sh and entered fsck.
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Can't open /dev/ar0a: Device not configured
Can't open /dev/ar0f: Device not configured
Can't open /dev/ar0e: Device not configured
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From there I am just at a # prompt, presumably in /bin/sh

I think I know what is going on. The startup is configured to look for the device 'ar' but I am running one called 'ad'. ad0 through ad3 are the two ide interfaces so that won't help. I really have no experience with Unix but I believe it is as simple as either somehow renaming (or moving?) the device so it is called 'ar0' or changing the references in the loader to 'ad4'.

Does anyone have any suggestions? Thanks in advance.