This was caused by reusing ASM disks from a previous installation of GI. Remedied this with the following commands:
[root@redfern1 ~]# dd if=/dev/zero of=/dev/sda1 bs=32768 count=32768 conv=notrunc oflag=direct
32768+0 records in
32768+0 records out
1073741824 bytes (1.1 GB) copied, 49.9376 s, 21.5 MB/s
[root@redfern1 ~]# dd if=/dev/zero of=/dev/sdb1 bs=32768 count=32768 conv=notrunc oflag=direct
32768+0 records in
32768+0 records out
1073741824 bytes (1.1 GB) copied, 52.2119 s, 20.6 MB/s
[root@redfern1 ~]# dd if=/dev/zero of=/dev/sdc1 bs=32768 count=32768 conv=notrunc oflag=direct
32768+0 records in
32768+0 records out
1073741824 bytes (1.1 GB) copied, 50.1007 s, 21.4 MB/s
[root@redfern1 ~]# dd if=/dev/zero of=/dev/sdd1 bs=32768 count=32768 conv=notrunc oflag=direct
32768+0 records in
32768+0 records out
1073741824 bytes (1.1 GB) copied, 49.6538 s, 21.6 MB/s
[root@redfern1 ~]# dd if=/dev/zero of=/dev/sde1 bs=32768 count=32768 conv=notrunc oflag=direct
32768+0 records in
32768+0 records out
1073741824 bytes (1.1 GB) copied, 49.7564 s, 21.6 MB/s
However, this caused the ASM initialisation of disks to fail with:
[root@redfern1 ~]# /sbin/oracleasm createdisk DATA /dev/sdb1
Writing disk header: done
Instantiating disk: failed
Clearing disk header: done
Scanning for ASM disks had the effect of clearing this problem:
[root@redfern1 ~]# oracleasm scandisks
Reloading disk partitions: done
Cleaning any stale ASM disks...
Cleaning disk "DATA"
Cleaning disk "FRA"
Cleaning disk "REDO1"
Cleaning disk "REDO2"
Cleaning disk "VOTE"
Scanning system for ASM disks...
Scanning again had no effect:
[root@redfern1 ~]# oracleasm scandisks
Reloading disk partitions: done
Cleaning any stale ASM disks...
Scanning system for ASM disks...
Now, ASM initialisation of the disk worked:
[root@redfern1 ~]# /sbin/oracleasm createdisk DATA /dev/sdb1
Writing disk header: done
Instantiating disk: done