voldisk command failing with "disk read failure"

Greetings. 

We have an alphaserver ES40 running T64 v5.1a on which a disk was
failing.
The disk is half of a mirror. We removed the disk:

voldg -g userdg -k rmdisk userdg03
voldisk rm dsk4c

replaced it, scanned the bus (hwmgr scan scsi), found the new disk at
dsk6, did:

dsfmgr -e dsk6 dsk4 

to move replacement to the old location.

We then put the disklabel back on by zeroing "disklabel -z", then
copying a label from its mirror partner and using "disklabel -R dsk4
/tmp/otherdiskfile". We also edited the label to set it from "LSMsimp"
to "unused".

So far so good. Now, however, we can't do anything with the disk:

voldisk -f init dsk4a
lsm:voldisk: ERROR: Device dsk4a: define failed:
        Disk read failure

It's like the disk is there, OS sees it, but somehow it's unavailable to
LSM. Yesterday, had similar problems on another alpha, had to reboot to
make disk fully available, leading me to wonder if it's a patch issue.

In any event, does anyone know of a way to make this disk more fully
accessible so we can put it back in the mirror *without* the reboot?

TIA!

Judith Reed