Use with your own risk, but this is works

Req:
-Metadevice : d56
-Disk: emcpower6a(A2=c3t500601623021B12Ed2s2) + emcpower8a(A2=c3t500601623021B12Ed8s2)

Command:

# df -h |grep d56
/dev/md/dsk/d56 391G 64M 390G 1% /archive1

# metastat d56
d56: Soft Partition
Device: c3t500601623021B12Ed2s2
State: Okay
Size: 832421888 blocks (396 GB)
Device Start Block Dbase Reloc
c3t500601623021B12Ed2s2 16384 No Yes

# metaclear d56
d56: Soft Partition is cleared

# metainit d56 2 1 emcpower6a 1 emcpower8a
d56: Concat/Stripe is setup

# mount /dev/md/dsk/d56 /archive1
# growfs -M /archive1 /dev/md/rdsk/d56
# df -h|grep d56
/dev/md/dsk/d56 788G 64M 787G 1% /archive1

# metastat d56
d56: Concat/Stripe
Size: 1677639680 blocks (799 GB)
Stripe 0:
Device Start Block Dbase Reloc
emcpower6a 0 No No
Stripe 1:
Device Start Block Dbase Reloc
emcpower8a 16384 No No

Device Relocation Information:
Device Reloc Device ID
emcpower6a No -
emcpower8a No -