Less Known Solaris features: Jumpstart Enterprise Toolkit - Part 11: Mirrored boot disks
Okay, in enterprise computing you wouldn´t use a system without redundant boot disks (at least, when you haven´t an application that can survive a loss of computing nodes without a problem). So it would be nice to automatically configure a mirror of the boot disks with the Solaris Volume Manager. I assume in the following part, that you have a working knowledge with the SVM. When this not the case, it isn´t really a big problem, as this part it somewhat selfexplaining when you are aware of the concept of RAID.
At first you have to include the
sds module to the
base_config_product line. Then choose the disk you want to use for mirroring, in my case it´s
/dev/dsk/c1d1. Line 4 orders the
sds module to copy the vtoc of the first mirror to the second one. When there are only two disks in your system you have to specify the
sds_mirror_root_flag with yes in line 10. Solaris Volume Manager want to see the metadb replica copies on at least three disks.When you want to find out the correct state of an situation you need at least three copies to be sure. With only two copies, one or the other version may be correct, with three you have two correct copies, so there is a good chance that the two copies represent the correct state. Solaris Volume Manager likes to distribute those over at least three disk to ensure that the failure of a disk won´t take out exactly the half of the copies. You have to tell the system that it shouldn´t obey this rule.
sds_mirror_root_flag specifies that.
Effects of the configuration
Okay, after the installation we can log into the system. You may notice after the installation a vast amount of accesses to the harddisk. The devices for
/ and the
swap are not longer referenced by an device name. Instead of this you will find the names of the logical devices of the Solaris Volume Manager.
Let´s look after the exact configuration of the volume manager.
The default numbering scheme for the solaris volume manager is quite simple: The mirror is designated with the first number in a decade (e.g. 10,20,30), the parts of a mirror are numbered with the next free numbers in the decade. For example: The first mirror half of the first mirror get the number 11, the second number gets the number 12. It takes a while until the mirrors are in sync, but after this you have a automatically installed, patched, customized and mirrored system.