mdadm cannot open devices

Just assembled a new Fedora 9 machine - md1-5 created OK, but am having trouble putting md6 together - machine rebooted after partitioning):

[root@hugo2 ~]# mdadm -C /dev/md6 -l 1 -n 2 /dev/sda1 /dev/sdb1
mdadm: Cannot open /dev/sda1: No such device or address
mdadm: Cannot open /dev/sdb1: No such device or address
mdadm: create aborted

dmesg:

------------------------------------------------

scsi0 : sata_sil
scsi1 : sata_sil
ata1: SATA max UDMA/100 mmio m512@0xf0401000 tf 0xf0401080 irq 21
ata2: SATA max UDMA/100 mmio m512@0xf0401000 tf 0xf04010c0 irq 21
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
ata1.00: ATA-8: ST31000340NS, SN05, max UDMA/133
ata1.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 0/32)
ata1.00: configured for UDMA/100
ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
ata2.00: ATA-8: ST31000340NS, SN05, max UDMA/133
ata2.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 0/32)
ata2.00: configured for UDMA/100
scsi 0:0:0:0: Direct-Access     ATA      ST31000340NS     SN05 PQ: 0 ANSI: 5
sd 0:0:0:0: [sda] 1953525168 512-byte hardware sectors (1000205 MB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sd 0:0:0:0: [sda] 1953525168 512-byte hardware sectors (1000205 MB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
 sda: sda1
sd 0:0:0:0: [sda] Attached SCSI disk
scsi 1:0:0:0: Direct-Access     ATA      ST31000340NS     SN05 PQ: 0 ANSI: 5
sd 1:0:0:0: [sdb] 1953525168 512-byte hardware sectors (1000205 MB)
sd 1:0:0:0: [sdb] Write Protect is off
sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sd 1:0:0:0: [sdb] 1953525168 512-byte hardware sectors (1000205 MB)
sd 1:0:0:0: [sdb] Write Protect is off
sd 1:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
 sdb: sdb1
sd 1:0:0:0: [sdb] Attached SCSI disk

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[root@hugo2 ~]# fdisk /dev/sda

The number of cylinders for this disk is set to 121601.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x2ef7934e

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1      121585   976631481   83  Linux


Kernel is 2.6.25-14.fc9.i686 and mdadm is mdadm-2.6.4-4.fc9.i386.

Thanks,

Richard