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NAME

lvcreate — create logical volume in LVM volume group

SYNOPSIS

/usr/sbin/lvcreate [-A autobackup] [-c mirror_consistency] [-C contiguous] [-d schedule] [-D distributed] [-i stripes -I stripe_size] [-l le_number | -L lv_size] [-m mirror_copies] [-M mirror_write_cache] [-n lv_name] [-p permission] [-r relocate] [-s strict] vg_name

Remarks

Mirrored disk operations require the installation of the optional HP MirrorDisk/UX software, which is not included in the standard HP-UX operating system.

lvcreate cannot be performed if the volume group is activated in shared mode.

Logical volumes that were created using the striped option are not supported in shared mode.

DESCRIPTION

The lvcreate command creates a new logical volume within the volume group specified by vg_name. Up to 255 logical volumes can be created in one volume group.

If you specify the -n lv_name option, a new logical volume is created with that name. Otherwise, a system-generated name of the form lvolN is created, where N is the decimal equivalent of the two least significant bytes of the minor number of the new logical volume, in the range 1 to 255 (see lvm(7)). Two device files are created in vg_name: a block device file named lv_name or lvolN, and a character (raw) device file named rlv_name or rlvolN.

If you omit the -l and -L options, the logical volume is created with zero length. This permits you to choose its physical volume location when you allocate logical extents with the lvextend command (see lvextend(1M)). If you specify -l or -L, the location is determined automatically.

The default settings provide the most commonly used characteristics. Use the options to tailor the logical volume to the requirements of the system. Once a logical volume is created, some of its characteristics can be changed with the lvchange, lvextend, and lvreduce commands (see lvchange(1M), lvextend(1M), and lvreduce(1M)).

Options and Arguments

The -c, -d, -m, -M, and -s options are only meaningful if the optional HP MirrorDisk/UX software has been installed on the system.

lvcreate recognizes the following options and arguments:

vg_name

The path name of a volume group.

-A autobackup

Set automatic backup for this invocation of this command. autobackup can have one of the following values:

y

Automatically back up configuration changes made to the logical volume. This is the default.

After this command executes, the vgcfgbackup command (see vgcfgbackup(1M)) is executed for the volume group to which the logical volume belongs.

n

Do not back up configuration changes this time.

-c mirror_consistency

Set mirror consistency recovery. This option is effective only when -M n is specified. It is ignored for -M y. mirror_consistency can have one of the following values:

y

Set mirror consistency recovery on. This is the default.

LVM achieves mirror consistency during volume group activation by going through all logical extents and copying data from a nonstale copy to the other mirror copies.

n

Set mirror consistency recovery off. LVM does not perform mirror consistency recovery on this logical volume when the volume group is activated.

-C contiguous

Set the contiguous allocation policy. A contiguous logical volume has three characteristics:

  • Physical extents are allocated in ascending order,

  • No gap is allowed between physical extents within a mirror copy,

  • Physical extents of any mirror copy all reside on a single physical volume.

Use the strict (-s) and contiguous (-C) options together to form various combined allocation policies on a logical volume. For example, -s y -C y defines a logical volume such that each mirror copy is contiguous, yet mirror copies of a logical extent cannot share the same physical volume.

contiguous can have one of the following values:

y

Set a contiguous allocation policy.

n

Do not set a contiguous allocation policy. This is the default.

-d schedule

Set the scheduling policy when a logical extent with more than one mirror is written. (The scheduling policy of a striped logical volume is striped and cannot be changed.) schedule can have one of the following values:

p

Establish a parallel scheduling policy. This is the default.

s

Establish a sequential scheduling policy. Use this value with care, because it leads to performance loss in most cases.

-D distributed

Set the distributed allocation policy. distributed can have one of the following values:

y

Turn on distributed allocation.

n

Turn off distributed allocation. This is the default.

When the distributed allocation policy is turned on, only one free extent is allocated from the first available physical volume. The next free extent is allocated from the next available physical volume. Allocation of free extents proceeds in round-robin order on the list of available physical volumes.

When the distributed allocation policy is turned off, all available free extents are allocated from each available physical volume before proceeding to the next available physical volume. This is the default.

The distributed allocation policy REQUIRES the PVG-strict allocation policy ( -s g ) to ensure that mirrors of distributed extents do not overlap (for maximum availability).

lvcreate(1M) will obtain the list of available physical volumes from /etc/lvmpvg. See vgextend(1M) for more information on physical volume groups and /etc/lvmpvg.

When a logical volume with distributed extents is mirrored, the resulting layout is commonly referred to as EXTENT-BASED MIRRORED STRIPES.

Note that EXTENT-BASED MIRRORED STRIPES can be created without the distributed allocation policy by adding one extent at a time to the desired physical volumes through lvextend(1M).

The distributed allocation policy is incompatible with the striped scheduling policy ( -i stripes ) and the contiguous allocation policy ( -C y ).

The lvchange(1M) command can be used to assign the distributed allocation policy to an existing logical volume.

See lvdisplay(1M) for display values.

See EXAMPLES.

-i stripes

Set the number of disks to stripe across. stripes must be in the range 2 to the number of disks in the current volume group. -i and -I must be specified together.

-I stripe_size

Set the size in kilobytes of the stripe. stripe_size should be a power of 2 in the range 4 to 32768. -i and -I must be specified together.

-l le_number

Allocate space to the logical volume, specified in logical extents. le_number is a decimal value in the range 1 to 65535 (the implementation limit). The default is described above.

Either -l or -L can be specified, but not both.

-L lv_size

Allocate space to the logical volume, specified in megabytes. lv_size is a decimal value in the range 1 to 16777216 (the implementation limit). lv_size is rounded up to the nearest multiple of the logical extent size, equivalent to the physical extent size defined for the volume group by the vgcreate command (see vgcreate(1M)). The default is described above.

Either the -l or the -L option can be specified, but not both.

-m mirror_copies

Set the number of mirror copies allocated for each logical extent. A mirror copy contains the same data as the original. mirror_copies can have the value 1 or 2. The default value is 0 (no mirror copies).

-M mirror_write_cache

Set the Mirror Write Cache flag. mirror_write_cache can have one of the following values:

y

Set Mirror Write Cache on. This is the default.

Every write to a mirror copy is recorded in the Mirror Write Cache. The Mirror Consistency Record in the Volume Group Reserved Area on the disk is updated whenever there is a write to a logical track group that is not already recorded in the cache. This allows LVM to determine whether all the mirror copies are identical, even across system crashes. When the volume group is activated, the Mirror Consistency Record is used to perform mirror consistency recovery.

n

Set Mirror Write Cache to off. Mirror write does not incur an additional write to the Mirror Consistency Record.

-n lv_name

Set the name of the new logical volume to lv_name, where lv_name is a simple file name, not a path name. The default is described above.

-p permission

Set the access permission. permission can have one of the following values:

w

Set the access permission to read-write. This is the default.

r

Set the access permission to read-only.

-r relocate

Set the bad block relocation policy. relocate can have one of the following values:

y

Allow bad block relocation. Upon a media failure (detection of a bad block of data on disk), LVM will mark the failed block in the Bad Block Directory, and attempt to relocate the block to a new location on disk. If relocation is successful then no error will be returned, and future I/O requests which contain the bad block will be directed to the new location. If relocation is unsuccessful, an I/O error will be returned, and subsequent I/O requests containing the bad block will again attempt relocation. This is the default.

n

Prevent bad block relocation. Upon a media failure, LVM will mark the failed block as bad in the Bad Block Directory, but will NOT attempt to relocate the bad block to a new location on disk. Future I/O requests which contain the bad block will return with an I/O error. No attempt will be made to access the bad block.

N

Disable bad block relocation and the Bad Block Directory. Upon a media failure, LVM will NOT attempt to relocate the bad block. In addition it will NOT enter the block in the Bad Block Directory. LVM will have no record of the block being bad, and will attempt to access it on future I/O requests.

-s strict

Set the strict allocation policy. Mirror copies of a logical extent can be allocated to share or not share the same physical volume or physical volume group. strict can have one of the following values:

y

Set a strict allocation policy. Mirrors of a logical extent cannot share the same physical volume. This is the default.

g

Set a PVG-strict allocation policy. Mirrors of a logical extent cannot share the same physical volume group. A PVG-strict allocation policy cannot be set on a logical volume in a volume group that does not have a physical volume group defined.

n

Do not set a strict or PVG-strict allocation policy. Mirrors of a logical extent can share the same physical volume.

Striped logical volumes are only allocated using the strict or PVG-strict allocation policies. The number of extents for a striped logical volume is always a multiple of the number of disks the logical volume is striped across. A logical volume striped across n disks, is allocated in sets of n extents, and each extent of a given set is allocated on a different physical volumes in the volume group.

EXTERNAL INFLUENCES

Environment Variables

LANG determines the language in which messages are displayed.

If LANG is not specified or is null, it defaults to "C" (see lang(5)).

If any internationalization variable contains an invalid setting, all internationalization variables default to "C" (see environ(5)).

EXAMPLES

Create a logical volume in volume group /dev/vg02:

lvcreate /dev/vg02

Create a logical volume in volume group /dev/vg03 with nonstrict allocation policy:

lvcreate -s n /dev/vg03

Create a logical volume of size 100 MB in volume group /dev/vg03:

lvcreate -L 100 /dev/vg03

Create a logical volume of size 90 MB striped across 3 disks with a stripe size of 64 KB:

lvcreate -L 90 -i 3 -I 64 /dev/vg03

Distributed Allocation Policy

This example shows how the -D y option can be used to create EXTENT-BASED MIRRORED STRIPES.

Assume that volume group /dev/vgtest has two physical volume groups: pvg1, pvg2.

Assume that each physical volume group has 2 physical volumes.

Assume that the first physical volume in each pvg has 3 extents free and the second physical volume in each pvg has 2 extents free.

The following command creates a logical volume in vgtest with EXTENT-BASED MIRRORED STRIPES:

lvcreate -D y -s g -m 1 -l 5 /dev/vgtest

The distributed allocation proceeds as follows:

  • A free extent is allocated from the 1st pvol in pvg1.

  • A free extent is allocated from the 2nd pvol in pvg1.

  • A free extent is allocated from the 1st pvol in pvg1.

  • A free extent is allocated from the 2nd pvol in pvg1.

  • A free extent is allocated from the 1st pvol in pvg1.

  • Mirrors for the five extents are then allocated from the free extents in pvg2 in a similar manner.

WARNINGS

The -m and -r options cannot be used with HP-IB devices.

The root, swap, and dump logical volumes (see lvlnboot(1M)) must be created with contiguous allocation policy.

SEE ALSO

lvchange(1M), lvdisplay(1M), lvextend(1M), lvreduce(1M), pvchange(1M).



lvchange
  		 


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