Creating Plexed Logical Volumes for Root

Caution: The procedure in this section can result in the loss of data if it is not performed properly. It is recommended only for experienced IRIX system administrators. You can put your Root filesystem on a plexed volume for greater reliability. A plexed Root volume allows your system to continue running even if one of the root disks fails. If there is a separate Usr filesystem on the system disk, it should be plexed, too. Because the swap partition may be unavailable if the root disk fails, a spare swap partition should available on a different disk. Administering the plexes of the Root and, if present, Usr volumes and the swap partitions is easiest if each disk used in the volumes is identical and is partitioned identically.

The Root volume can contain only a data subvolume. Each plex of the data subvolume can contain only a single volume element. The volume element must contain a single disk partition.

The Root filesystem can be either an EFS filesystem or an XFS filesystem with an internal log.

Use the following procedure to create a plexed Root volume. It assumes that you are starting with a working system (not a system with an empty system disk).

1. Make the root partition into an XLV volume. In this example, the XLV volume is called xlv_root:

   # xlv_make

   xlv_make> vol xlv_root

   xlv_root

   xlv_make> data

   xlv_root.data

   xlv_make> ve -force /dev/dsk/dks0d1s0

   xlv_root.data.0.0

   xlv_make> end

   Object specification completed

   xlv_make> exit

   Newly created objects will be written to disk.

   Is this what you want?(yes) yes

   Invoking xlv_assemble

   The result is an XLV volume named xlv_root that contains the root partition. Since XLV preserves the data in partitions, the contents of the root partition are preserved. The -force option to the ve command was used because a mounted partition was included in the volume.

2. Reboot the system so that the system switches from running off the root partition at /dev/dsk/dks0d1s0 to running off the logical volume /dev/dsk/xlv/xlv_root:

   # reboot

3. You can confirm that the Root volume is being used by comparing the major and minor device numbers of /dev/root and /dev/dsk/xlv/xlv_root:

# ls -l /dev/root /dev/dsk/xlv/xlv_root
brw-------    2 root     sys      192,  0 Oct 31 17:58 /dev/root
brw-------    2 root     sys      192,  0 Dec 12 17:58 /dev/dsk/xlv/xlv_root

1. Create the second plex, for example out of /dev/dsk/dks0d2s0, and call the plex root_plex1:

   # xlv_make

   xlv_make> plex root_plex1

   root_plex1

   xlv_make> ve /dev/dsk/dks0d2s0

   root_plex1.0

   xlv_make> end

   Object specification completed

   xlv_make> exit

   Newly created objects will be written to disk.

   Is this what you want?(yes) yes

   Invoking xlv_assemble

2. Add sash to the volume header of the disk used for the second plex. It enables booting off of the alternate plex if the primary plex fails.

   # dvhtool -v get sash /tmp/sash /dev/rdsk/dks0d1vh

   # dvhtool -v add /tmp/sash sash /dev/rdsk/dks0d2vh

3. Attach the second plex to the volume using xlv_mgr and quit out of xlv_mgr:

   # xlv_mgr

   xlv_mgr> attach plex root_plex1 xlv_root.data

   xlv_mgr> quit

   When the shell prompt returns, the system automatically begins a plex revive so that the two plexes contain the same data.

4. Add procedure for creating Boot volume.