/etc/ccd.conf:

ccd0    0       none    /dev/wd1a /dev/wd2a

fdisk wd1

Disk: wd1       geometry: 1653/255/63 [26555445 Sectors]
Offset: 0       Signature: 0xAA55
         Starting       Ending       LBA Info:
 #: id    C   H  S -    C   H  S [       start:      size   ]
------------------------------------------------------------------------
 0: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
 1: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
 2: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
*3: A6    0   1  1 - 1652 254 63 [          63:    26555382 ] OpenBSD


fdisk wd2

Disk: wd2       geometry: 1655/255/63 [26587575 Sectors]
Offset: 0       Signature: 0xAA55
         Starting       Ending       LBA Info:
 #: id    C   H  S -    C   H  S [       start:      size   ]
------------------------------------------------------------------------
 0: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
 1: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
 2: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
*3: A6    0   1  1 - 1654 254 63 [          63:    26587512 ] OpenBSD


disklabel wd1

# Inside MBR partition 3: type A6 start 63 size 26555382
# /dev/rwd1c:
type: ESDI
disk: ESDI/IDE disk
label: WDC WD136AA-35BA
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 16383
total sectors: 26564832
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

16 partitions:
#             size        offset  fstype [fsize bsize  cpg]
  a:      26555382            63     ccd                   # Cyl     0*- 26344*
  c:      26564832             0  unused      0     0      # Cyl     0 - 26353

# Inside MBR partition 3: type A6 start 63 size 26587512
# /dev/rwd2c:
type: ESDI
disk: ESDI/IDE disk
label: Maxtor 91360U4
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 16383
total sectors: 26588016
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

16 partitions:
#             size        offset  fstype [fsize bsize  cpg]
  a:      26587512            63     ccd                   # Cyl     0*- 26376*
  c:      26588016             0  unused      0     0      # Cyl     0 - 26376