In a general production environment you’ll find the OS root disk is mirrored to avoid any single point of failures. Its is important to know how to find the primary and alternate boot device to troubleshoot in some cases. You can either identify the boot device from the OK prompt (in case of a SPARC machine) or when the OS is booted up.
SPARC
Identifying boot device at OK prompt
To identify the boot device at OK prompt :
ok> printenv boot-device boot-device = rootdisk mirrordisk
Here the primary boot device is set to a device alias, “rootdisk”. The alternate boot device is specified using the devalias mirrordisk. So the system first looks for the disk with alias rootdisk and if its not bootable it goes for the 2nd disk i.e. the mirrordisk. Use the devalias command to see the physical device path for the boot-device:
ok> devalias screen /pci@1f,0/SUNW,m64B@13 net /pci@1f,0/network@c,1 cdrom2 /pci@1f,0/ide@d/cdrom@2,0:f cdrom1 /pci@1f,0/ide@d/cdrom@1,0:f cdrom /pci@1f,0/ide@d/cdrom@1,0:f rootdisk /pci@1f,0/ide@d/disk@0,0 -- the physical path to the 'rootdisk' alias mirrordisk /pci@1f,0/ide@d/disk@3,0 -- the physical path to the 'mirrordisk' alias disk2 /pci@1f,0/ide@d/disk@2,0 disk1 /pci@1f,0/ide@d/disk@1,0 disk0 /pci@1f,0/ide@d/disk@0,0 ide /pci@1f,0/ide@d floppy /pci@1f,0/isa@7/dma/floppy ttyb /pci@1f,0/isa@7/serial@0,2e8 ttya /pci@1f,0/isa@7/serial@0,3f8 name aliases
Note : Here the physical device is rootdisk /pci@1f,0/ide@d/disk@0,0. In case if boot-device is set wrong, we can either boot from CDROM or in single user mode to identify the correct boot device from the OS command line.
Identifying boot device using OS command line
Using the eeprom command
We can also find out the boot device using the operating system commands. Use the eeprom command to find the boot device :
# eeprom | grep boot-device boot-device=rootdisk mirror-disk
Here, again the primary boot-device is a devalias “rootdisk”, So in order to find out the physical path of the primary boot disk use :
# prtconf -vp | grep 'rootdisk':
rootdisk: '/pci@1f,0/ide@d/disk@0,0'
To find the logical device name of the rootdisk, we can use the format command :
# format Searching for disks...done AVAILABLE DISK SELECTIONS: 0. c0t0d0 [ST320414A cyl 39533 alt 2 hd 16 sec 63] /pci@1f,0/ide@d/dad@0,0 -- the logical device c0t0d0 is the same physical device as the 'rootdisk' alias from prtconf -vp 1. c0t2d0 [DEFAULT cyl 39533 alt 2 hd 16 sec 63] /pci@1f,0/ide@d/dad@2,0
Similarly you can find the mirrordisk physical path.
x86 / x64
x86 machines uses BIOS instead of the OBP so to duplicate the functionality of eeprom in SPARC machine, x86 systems uses a file /boot/solaris/bootenv.rc at boot time. To find out the primary and alternate boot disk from eeprom :
# eeprom |grep boot bootpath=/pci@0,0/pci15ad,1976@10/sd@0,0:a altbootpath=/pci@0,0/pci15ad,1976@10/sd@1,0:a
Also when the system is booted up you can see the 2 different boot options to select from. Below is a screen shot of mirrored boot disk under veritas volume manager.
