How to create a dummy disk to reserve an hdisk number?
Below you find a situation where the next LUN that is mapped to your system would get an hdisk number 0 (hdisk0):
# lsdev -Cc disk
hdisk1 Available 06-08-00-4,0 16 Bit LVD SCSI Disk Drive
hdisk2 Available 06-08-00-5,0 16 Bit LVD SCSI Disk Drive
To avoid this you could reserve hdisk0 for a dummy disk, e.g.:
# mkdev -l hdisk0 -c disk -t osdisk -s scsi -p scsi0 -w 0,10 -d
hdisk0 defined
Now we see hdisk0 as defined:
# lsdev -Cc disk
hdisk0 Defined 06-08-00-0,10 Other SCSI Disk Drive
hdisk1 Available 06-08-00-4,0 16 Bit LVD SCSI Disk Drive
hdisk2 Available 06-08-00-5,0 16 Bit LVD SCSI Disk Drive
... and the next LUN would be mapped to hdisk3.
Unfortunately this trick only works for systems with a SAS controller assigned. With AIX 5.3 you still have the option to create a dummy SSA disk:
# mkdev -l hdisk0 -p ssar -t hdisk -w dummy
mkdev: 0514-519 The following device was not found in the customized
device configuration database:
name='ssar'
Don't be confused by the error - we have a hdisk0 now:
# lsdev -Cc disk
hdisk0 Defined SSA Logical Disk Drive
hdisk1 Available 06-08-00-4,0 16 Bit LVD SCSI Disk Drive
hdisk2 Available 06-08-00-5,0 16 Bit LVD SCSI Disk Drive
This complicated procedure is not needed any more since AIX 7.1 and AIX 6.1 TL6 - a new command has been made available:
# lspv
hdisk0 00c8b12ce3c7d496 rootvg active
hdisk1 00c8b12cf28e737b None
# rendev -l hdisk1 hdisk99
# lspv
hdisk0 00c8b12ce3c7d496 rootvg active
hdisk99 00c8b12cf28e737b None