The file /etc/lvtab contains a table of logical volumes. It is read by the commands that create, install, and check the consistency of logical volumes. You can modify it with a text editor to add new logical volumes or to change existing ones.

The entries in /etc/lvtab have this form (it is shown wrapped here, but it is a single line with no blank spaces):

volume_device_name:[volume_name][:stripes=stripe_number[:step=stripe_unit]]:devs=
device_pathnames 

The volume_device_name is of the form lvn, where n is a one or two digit integer. The logical volume is accessed through the device special files /dev/dsk/lv<n> and /dev/rdsk/lv<n>.

The volume_name is an arbitrary identifying name for the logical volume. This name is included in the logical volume labels on each of the partitions making up the logical volume. It is then used by commands to verify that the logical volume on the disks is actually the volume expected by /etc/lvtab. Any name of up to 80 characters can be used; you should probably choose something that other users can identify. You can leave this field blank, but this is not recommended.

The stripes option creates a logical volume that is striped across its constituent devices (see Figure 6-1 for an illustration of how the data is written to the devices). The number of device_pathnames must be a multiple of stripe_number. stripe_number specifies the number of disks the volume is striped across. For example, suppose you have a logical volume with 6 constituent devices and a stripe_number of 3. The logical volume is set up to stripe across the first three devices until they are filled, then to stripe across the second three.

The step option further specifies the stripe unit (the granularity with which the storage is distributed across the components of a striped volume). stripe_unit is measured in disk blocks. The default stripe unit is the device track size, which is generally a good value to use.

The device_pathnames are listed following any options. They are the block device filenames of the devices constituting the logical volume. device_pathnames must be separated by commas. The partitions named must be legal for use as normal data storage, and not dedicated partitions, such as swap.

The mklv command creates logical volumes by writing logical volume labels for the devices that will make up the volume. The basic mklv command is:

# mklv volume_device_name 

mklv reads the entry in /etc/lvtab identified by volume_device_name (volume_device_name is the first field in the /etc/lvtab file) and creates the logical volume described. It labels the devices appropriately by writing logical volume labels in the volume headers of the disks used in the logical volume, then initializes the logical volume device for use. It is not necessary to run the lvinit command after running mklv.

Normally, mklv checks all the named devices to see if they are already part of a logical volume or contain a filesystem. The option -f forces mklv to skip those checks.

Various errors can arise when trying to create a logical volume. For example, one of the specified disks might be missing, the new lvtab entry might have a typographical error, or the partitions of a striped volume might not be exactly the same size.

If the partitions aren't exactly the same size, for example because the default partitioning for drives of similar sizes but from different manufacturers is slightly different, you will see an error message similar to this from mklv:

lv0:proj:stripes=2:devs= \ 
        /dev/dsk/dks0d2s7,  \ 
        /dev/dsk/dks1d0s7 <INCORRECT PARTITION SIZE> 

In this case, you need to adjust the partition sizes; see the section “Repartitioning a Disk With fx” in Chapter 2 for instructions.

The mklv(1M) reference page describes the possible error messages and their meanings.

As described in the section “lv Logical Volumes” in Chapter 6, the lvck command is used to check the consistency of logical volumes.

To check every logical volume for which there is an entry in /etc/lvtab, give this command:

# lvck 

To check only one entry in /etc/lvtab, give the name of a logical volume device (the first field in the /etc/lvtab entry), for example:

# lvck lv0 

The -d option of lvck facilitates re-creation of an lvtab for the system, if necessary. You might use this option if, for example, /etc/lvtab became corrupted or if you somehow lost track of which disks were connected during a system reconfiguration. With the -d flag, lvck ignores /etc/lvtab and searches through all disks connected to the system in order to locate all logical volumes present. It prints a description of each logical volume found in a form resembling an lvtab entry. For example:

# lvck -d 
# The following logical volumes are present and correct: 

# Volume id:   IRIX: Mon Jun  5 16:58:15 1995

lv?:Zebra Project:devs=/dev/dsk/dks0d2s0,       \        /dev/dsk/dks0d3s0
...

lvck can print out any logical volume label that exists for a block device file. The output resembles an lvtab entry. This mode of lvck is purely informational; no checks are made of any other devices mentioned in the logical volume label. To print the label, invoke lvck with the block device file, for example:

# lvck /dev/dsk/dks0d2s7 

# Volume id:   IRIX: Thu Oct  5 16:29:33 1995

lv?:Project Data:devs=/dev/dsk/dks0d2s7,        \
        /dev/dsk/dks0d3s7

Possible errors and the messages from lvck are described in the lvck(1M) reference page.

Suppose that new disks are added to your system in order to provide additional storage. Instead of simply creating a filesystem on each disk, you could create a logical volume consisting of these new disks and make a filesystem on the logical volume. (To extend an existing filesystem onto a logical volume created out of an existing disk and the new disks, see the sections “Growing an EFS Filesystem Onto Another Disk” and “Growing an XFS Filesystem Onto Another Disk” in Chapter 4.)

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Caution: All files on the new disks are destroyed by this procedure. If the new disks contain files that you want to save, back up all files to tape or another disk before beginning this procedure.

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Follow this procedure to create a logical volume and a filesystem on new disks that have been initialized and partitioned:

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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.

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An existing logical volume can be extended to include one or more additional disk partitions. Remember that if the original logical volume is striped, you must add a number of disk partitions that is a multiple of the stripes parameter.

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Caution: All files on the disk partition added to the logical volume are destroyed. If the disk partition contains files that you want to save, back up all files on the partition to tape or another disk before beginning this procedure.

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Follow this procedure to increase the size of a logical volume, for example lv0:

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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.

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Follow this procedure to remove one or more partitions from a logical volume: