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.
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 following a system crash.
This setting
should only be used on logical volumes that do not require mirror consistency
recovery or where mirror consistency recovery is performed by another subsystem;
for example swap.
See the
WARNINGS
section for more details.
- -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.
The enforcement of a contiguous allocation policy via the
-C y
option is not supported on a striped logical volume.
- -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.
If
-i
is provided and
-I
is not, the stripe size is set to 8 kilobytes.
- -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.
If
-I
is provided and
-i
is not,
the command will fail and return an error.
Stripe size should be a value less than or equal to physical
extent size and must be specified with the
-i
option.
- -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 logical volume bad block relocation policy.
This is an obsolete flag available only to provide compatibility
with prior HP-UX releases.
The
relocate
flag can have one of the following values:
- y|n|N
This release does not provide the LVM bad block relocation feature;
but for compatibility reasons,
the value is maintained as a logical volume attribute.
Displaying the logical volume attributes will
show the value of the flag selected. However, regardless of the selection,
no new relocations will be done.
If the volume group is activated on a different HP-UX release that provides
the bad block relocation feature, bad blocks may be relocated depending
upon the value of this flag.
Although no new relocations will be done, any bad block relocations present
on a logical volume (activated on HP-UX releases that provided
this feature) will be honored when the volume group is activated
on this HP-UX release.
y
is the default value of this flag.
- -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 Volume considerations
Striped and mirrored logical volumes are supported.
A logical volume striped across
stripes
physical volumes is allocated in sets of
stripes
logical extents. A set corresponds to
stripes
physical extents if the volume is not mirrored or to
stripes
*
(mirror_copies
+ 1) physical extents if the volume is mirrored.
stripes
is the number of physical volumes the logical volume is striped across.
It is set with the option
-i
stripes.
mirror_copies
is the number of mirror copies allocated for each logical extent. It is
set with the
-m
option. The user data is striped across
stripes
physical extents of the set, and each of these extents is mirrored on
mirror_copies
other physical extents of the same set.
Striped logical volumes are only allocated using the
strict
or
PVG-strict
allocation policies.
Each physical extent of
a given set is allocated on
a different physical volume in the volume group.
The total number of physical extents
of a striped logical volume is always a multiple of
stripes
(or
stripes
*
(mirror_copies
+ 1) if the volume is mirrored).
A minimum of
stripes
(or
stripes
*
(mirror_copies
+ 1) if the volume is mirrored) physical volumes with adequate free space
and meeting the allocation policy is needed to allocate a striped logical
volume.
pvmove
cannot move extents of a striped logical volume.
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:
Create a logical volume in volume group
/dev/vg03
with non-strict allocation policy:
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
Create a logical volume of size 90 MB striped across 3 disks with one mirror
copy and a stripe size of 64 KB:
lvcreate -L 90 -i 3 -I 64 -m 1 /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
and
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 root, swap, and dump logical volumes (see
lvlnboot(1M))
must be created with contiguous allocation policy.
The creation of striped and mirrored logical volume(s) may prevent the import
and activation of the volume group on an earlier HP-UX release. See
lvcreate(1M)
on the earlier release to see if it explicitly states
that striping and mirroring is supported.
If the striped and mirrored
logical volumes of the volume group are removed or un-mirrored, the volume
group becomes again compatible with the older HP-UX releases.
By setting mirror consistency recovery off, crash recovery time will be reduced.
After a system crash the mirrored logical volume will be available,
but there may not be consistent data across each mirror copy.
The only types of data that can safely be put on a mirrored
logical volume with mirror consistency recovery turned off are:
data not needed after a crash, such as swap or other raw scratch data, or
data that an application itself will automatically reconstruct; for example,
a raw logical volume for which a database keeps a log of
incomplete transactions.
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