Written by {"display_name"=>"Joerg Moellenkamp", "login"=>"Joerg Moellenkamp", "email"=>"weblog@joerg.moellenkamp.org"}
on July 04, 2008

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.

# make_template -f -M -T togusa togusa sds<br />
Adding product configuration information for<br />
        + sds</blockquote>
</code>
<h3>Configuration in the template</h3>
As in the last example i will just include the interesting parts of the configuration. You have to modify some lines:<br />
<blockquote><code>base_config_products=" custom sbd sds"<br />
sds_product_version="default"<br />
sds_root_mirror="c1d1"<br />
sds_use_fmthard="yes"<br />
sds_database_locations="rootdisk.s7:3"<br />
sds_database_partition="s7:32"<br />
sds_metadb_size=""<br />
sds_root_alias="rootdisk"<br />
sds_root_mirror_devalias_name="rootmirror"<br />
sds_mirrored_root_flag="yes"

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.

-bash-3.2$ cat vfstab 
#device         device          mount           FS      fsck    mount   mount
#to mount       to fsck         point           type    pass    at boot options
#
fd      -       /dev/fd fd      -       no      -
/proc   -       /proc   proc    -       no      -
/dev/md/dsk/d20 -       -       swap    -       no      -
/dev/md/dsk/d10 /dev/md/rdsk/d10        /       ufs     1       no      logging
/devices        -       /devices        devfs   -       no      -
ctfs    -       /system/contract        ctfs    -       no      -
objfs   -       /system/object  objfs   -       no      -
swap    -       /tmp    tmpfs   -       yes     -

Let´s look after the exact configuration of the volume manager.

-bash-3.2$ metastat
d20: Mirror
    Submirror 0: d21
      State: Okay         
    Submirror 1: d22
      State: Okay         
    Pass: 1
    Read option: roundrobin (default)
    Write option: parallel (default)
    Size: 530145 blocks (258 MB)

d21: Submirror of d20
    State: Okay         
    Size: 530145 blocks (258 MB)
    Stripe 0:
        Device   Start Block  Dbase        State Reloc Hot Spare
        c0d0s1          0     No            Okay   Yes 


d22: Submirror of d20
    State: Okay         
    Size: 530145 blocks (258 MB)
    Stripe 0:
        Device   Start Block  Dbase        State Reloc Hot Spare
        c1d1s1          0     No            Okay   Yes 


d10: Mirror
    Submirror 0: d11
      State: Okay         
    Submirror 1: d12
      State: Okay         
    Pass: 1
    Read option: roundrobin (default)
    Write option: parallel (default)
    Size: 32836860 blocks (15 GB)

d11: Submirror of d10
    State: Okay         
    Size: 32836860 blocks (15 GB)
    Stripe 0:
        Device   Start Block  Dbase        State Reloc Hot Spare
        c0d0s0          0     No            Okay   Yes 


d12: Submirror of d10
    State: Okay         
    Size: 32836860 blocks (15 GB)
    Stripe 0:
        Device   Start Block  Dbase        State Reloc Hot Spare
        c1d1s0          0     No            Okay   Yes 


Device Relocation Information:
Device   Reloc  Device ID
c1d1   Yes      id1,cmdk@AVBOX_HARDDISK=VB37711a7b-00576cc9
c0d0   Yes      id1,cmdk@AVBOX_HARDDISK=VB97a90791-9d191449

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.

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