Unix Tip: Mirroring your root partition with Solaris Volume Manager

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Solaris Volume Manager can make easy work of mirroring your root file system, but you have to use the right commands in the right sequence to make easy work of this task. In this week's column, we'll run through each of the commands required to mirror root and show how you can check on what is happening in each step.

First, let's set the stage for our example system. We have a new Solaris 10 installation on a system with two internal disks and a disk array that we'll set up later. Each of the internal disks has been partitioned identically.

Part      Tag    Flag     Cylinders         Size            Blocks
  0       root    wm    1452 - 23167       29.92GB    (21716/0/0) 62737524
  1        var    wm   23168 - 24567        1.93GB    (1400/0/0)   4044600
  2     backup    wm       0 - 24619       33.92GB    (24620/0/0) 71127180
  3       swap    wu       0 -  1451        2.00GB    (1452/0/0)   4194828
  4 unassigned    wm       0                0         (0/0/0)            0
  5 unassigned    wm       0                0         (0/0/0)            0
  6 unassigned    wm       0                0         (0/0/0)            0
  7   reserved    wm   24568 - 24619       73.35MB    (52/0/0)      150228

The first thing we need to do is create the state database replicas. These are the data structures that store information about your volume configuration. We'll create multiple copies to ensure that we can recover if one copy becomes corrupt. You'll notice that we left a small partition for the state database replicas. We will now use the metadb -a -f command to create the replicas even if no database copies already exist. That -f option stands for "force".

# metadb -a -f c0t0d0s7 c0t1d0s7

In this example, we've only created two replicas, but you might want to create four or more to give you even better protection against potential problems. Database replicas can be created on dedicated slices or on slices that will become part of a concatenation or stripe.

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