Data will not be lost by booting from cd into single user:

Code:

 
boot cdrom -s

That will get you to a # prompt where you can:

Code:

fsck /dev/rdsk/c0t0d0s0

assuming c0t0d0s0 is your root disk. Otherwise, use appropriate device.

You can then mount the harddisk root filesystem to take a look at it:

Code:

mount /dev/dsk/c0t0d0s0 /a

Code:

 
cd /a

Code:

 
ls -l

'cd' into any directories you want to look at.

Make sure that you shutdown in an orderly manner after that:

Code:

init 0

No, you don't need to detach the mirror to do a fsck.