gmirror woes

[Brian McCann]

I had a disk die in a gmirror set, and I'm trying to replace it, but
I'm having a heck of a time.   I can see the mirror set in gmirror
list:

Geom name: gm0s1
State: DEGRADED
Components: 2
Balance: round-robin
Slice: 4096
Flags: NONE
GenID: 1
SyncID: 2
ID: 1250906373
Providers:
1. Name: mirror/gm0s1
   Mediasize: 36701166592 (34G)
   Sectorsize: 512
   Mode: r5w5e5
Consumers:
1. Name: da0s1
   Mediasize: 36701167104 (34G)
   Sectorsize: 512
   Mode: r1w1e1
   State: ACTIVE
   Priority: 0
   Flags: DIRTY
   GenID: 1
   SyncID: 2
   ID: 1129080348

But when I try to run gmirror configure -a mirror/gm0s1, I get:

No such device: mirror/gm0s1.

Can someone give me some pointers here?

Thanks,
--Brian