Question
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Needing to boot from a specific disk, use SMS to select the boot device.

Answer
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This is an example of booting into SMS mode on a pSeries machine in order to select a device to boot from.
To enter SMS mode, you can either press 1 when prompted by the system, or if the host is an LPAR attached to an HMC you can select the LPAR, pull down Operations -> Activate, then select Advanced -> Boot Mode -> SMS

To use 1 to get into SMS, press it when you see this screen:

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IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM
IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM IBM

1 = SMS Menu 5 = Default Boot List
8 = Open Firmware Prompt 6 = Stored Boot List
Memory Keyboard Network SCSI Speaker

At that time SMS will start up from firmware:

PowerPC Firmware
Version SF240_358
SMS 1.6 (c) Copyright IBM Corp. 2000,2005 All rights reserved.
——————————————————————————-
Main Menu

1. Select Language
2. Setup Remote IPL (Initial Program Load)
3. Change SCSI Settings
4. Select Console
5. Select Boot Options
——————————————————————————-
Navigation Keys:

X = eXit System Management Services
——————————————————————————-
Type menu item number and press Enter or select Navigation key: 5

Press 5 to select boot options

PowerPC Firmware
Version SF240_358
SMS 1.6 (c) Copyright IBM Corp. 2000,2005 All rights reserved.
——————————————————————————-
Multiboot
1. Select Install/Boot Device
2. Configure Boot Device Order
3. Multiboot Startup

Press 1 to select the boot device

PowerPC Firmware
Version SF240_358
SMS 1.6 (c) Copyright IBM Corp. 2000,2005 All rights reserved.
——————————————————————————-
Select Device Type
1. Diskette
2. Tape
3. CD/DVD
4. IDE
5. Hard Drive
6. Network
7. List all Devices

At this point you can either choose a specific boot device or let the firmware probe for all bootable devices. If 7 is chosen it will report back on any bootable adapters, and list any disks that are found to have an AIX boot image on them.

PowerPC Firmware
Version SF240_358
SMS 1.6 (c) Copyright IBM Corp. 2000,2005 All rights reserved.
——————————————————————————-
Select Device
Device Current Device
Number Position Name
1. – Virtual Ethernet
( loc=U9133.55A.105C2EH-V10-C2-T1 )
2. 1 SCSI 107374 MB FC Harddisk, part=2 (AIX 6.1.0)
( loc=U787B.001.DNWG2AB-P1-C2-T1-W200400a0b833530d-L0 )
3. 4 SCSI 107374 MB FC Harddisk, part=2 (AIX 6.1.0)
( loc=U787B.001.DNWG2AB-P1-C2-T1-W200500a0b833530d-L1000000000000 )

In this example I have chosen “List all Devices”, and after probing it finds 2 SAN-attached disks and one virtual Ethernet adapter. In this case hdisk0 is the disk in position 1 and hdisk1 is the disk in position 4.

Choosing device number 3 to boot from hdisk1, this menu will appear:

PowerPC Firmware
Version SF240_358
SMS 1.6 (c) Copyright IBM Corp. 2000,2005 All rights reserved.
——————————————————————————-
Select Task

SCSI 107374 MB FC Harddisk, part=2 (AIX 6.1.0)
( loc=U787B.001.DNWG2AB-P1-C2-T1-W200500a0b833530d-L1000000000000 )

1. Information
2. Normal Mode Boot
3. Service Mode Boot

To boot the system into Normal Mode (multiuser) choose option 2, or choose option 3 to boot into Maintenance Mode or Single User Mode from the selected device.