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NAME | DESCRIPTION | VDO TERMS | VDO USAGE | VDO TOPICS | SEE ALSO | COLOPHON |
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LVMVDO(7) Miscellaneous Information Manual LVMVDO(7)
lvmvdo — Support for Virtual Data Optimizer in LVM
VDO is software that provides inline block-level deduplication,
compression, and thin provisioning capabilities for primary
storage.
Deduplication is a technique for reducing the consumption of
storage resources by eliminating multiple copies of duplicate
blocks. Compression takes the individual unique blocks and shrinks
them. These reduced blocks are then efficiently packed together
into physical blocks. Thin provisioning manages the mapping from
logical blocks presented by VDO to where the data has actually
been physically stored, and also eliminates any blocks of all
zeroes.
With deduplication, instead of writing the same data more than
once, VDO detects and records each duplicate block as a reference
to the original block. VDO maintains a mapping from Logical Block
Addresses (LBA) (used by the storage layer above VDO) to physical
block addresses (used by the storage layer under VDO). After
deduplication, multiple logical block addresses may be mapped to
the same physical block address; these are called shared blocks
and are reference-counted by the software.
With compression, VDO compresses multiple blocks (or shared
blocks) with the fast LZ4 algorithm, and bins them together where
possible so that multiple compressed blocks fit within a 4 KB
block on the underlying storage. Mapping from LBA is to a physical
block address and index within it for the desired compressed data.
All compressed blocks are individually reference counted for
correctness.
Block sharing and block compression are invisible to applications
using the storage, which read and write blocks as they would if
VDO were not present. When a shared block is overwritten, a new
physical block is allocated for storing the new block data to
ensure that other logical block addresses that are mapped to the
shared physical block are not modified.
To use VDO with lvm(8), you must install the standard VDO user-
space tools vdoformat(8) and kernel module "dm_vdo" (For older
kernels <6.9 the out of tree kernel VDO module "kvdo" is
necessary).
The kernel module implements fine-grained storage virtualization,
thin provisioning, block sharing, compression and memory-efficient
duplicate identification. The user-space tools include vdostats(8)
for extracting statistics from VDO volumes.
VDODataLV
VDO data LV is a large hidden LV with the _vdata suffix.
It is created in a VG used by the VDO kernel target to
store all data and metadata blocks.
VDOPoolLV
VDO pool LV is a pool for virtual VDOLV(s), which are the
size of used VDODataLV. Only a single VDOLV is currently
supported.
VDOLV VDO LV is a virtual LV created from VDOPoolLV. Appears
blank after creation.
The primary methods for using VDO with lvm2:
1. Create a VDOPoolLV and a VDOLV
Create a VDOPoolLV that will hold VDO data, and a virtual size
VDOLV that the user can use. If you do not specify the virtual
size, then the VDOLV is created with the maximum size that always
fits into data volume even if no deduplication or compression can
happen (i.e. it can hold the incompressible content of
/dev/urandom). If you do not specify the name of VDOPoolLV, it is
taken from the sequence of vpool0, vpool1, ...
Note: The performance of TRIM/Discard operations is slow for large
volumes of VDO type. Please try to avoid sending discard requests
unless necessary because it might take considerable amount of time
to finish the discard operation.
lvcreate --type vdo -n VDOLV -L DataSize -V LargeVirtualSize
VG/VDOPoolLV
lvcreate --vdo -L DataSize VG
Example
# lvcreate --type vdo -n vdo0 -L 10G -V 100G vg/vdopool0
# mkfs.ext4 -E nodiscard /dev/vg/vdo0
2. Convert an existing LV into VDOPoolLV
Convert an already created or existing LV into a VDOPoolLV, which
is a volume that can hold data and metadata. You will be prompted
to confirm such conversion because it IRREVERSIBLY DESTROYS the
content of such volume and the volume is immediately formatted by
vdoformat(8) as a VDO pool data volume. You can specify the
virtual size of the VDOLV associated with this VDOPoolLV. If you
do not specify the virtual size, it will be set to the maximum
size that can keep 100% incompressible data in it.
lvconvert --type vdo-pool -n VDOLV -V VirtualSize VG/VDOPoolLV
lvconvert --vdopool VG/VDOPoolLV
Example
# lvconvert --type vdo-pool -n vdo0 -V10G vg/ExistingLV
3. Change the compression and deduplication of a VDOPoolLV
Disable or enable the compression and deduplication for VDOPoolLV
(the volume that maintains all VDO LV(s) associated with it).
lvchange --compression y|n --deduplication y|n VG/VDOPoolLV
Example
# lvchange --compression n vg/vdopool0
# lvchange --deduplication y vg/vdopool1
4. Change the default settings used for creating a VDOPoolLV
VDO allows you to set a large variety of options. Lots of these
settings can be specified in lvm.conf or profile settings. You can
prepare a number of different profiles in the /etc/lvm/profile
directory and just specify the profile file name. Check the
output of lvmconfig --type default --withcomments for a detailed
description of all individual VDO settings.
Example
# cat <<EOF > /etc/lvm/profile/vdo_create.profile
allocation {
vdo_use_compression=1
vdo_use_deduplication=1
vdo_minimum_io_size=4096
vdo_block_map_cache_size_mb=128
vdo_block_map_period=16380
vdo_use_sparse_index=0
vdo_index_memory_size_mb=256
vdo_slab_size_mb=2048
vdo_ack_threads=1
vdo_bio_threads=1
vdo_bio_rotation=64
vdo_cpu_threads=2
vdo_hash_zone_threads=1
vdo_logical_threads=1
vdo_physical_threads=1
vdo_max_discard=1
}
EOF
# lvcreate --vdo -L10G --metadataprofile vdo_create vg/vdopool0
# lvcreate --vdo -L10G --config 'allocation/vdo_cpu_threads=4' vg/vdopool1
5. Set or change VDO settings with option --vdosettings
Use the form 'option=value' or 'option1=value option2=value', or
repeat --vdosettings for each option being set. Options are
listed in the Example section above, for the full description see
lvm.conf(5). Options can omit 'vdo_' and 'vdo_use_' prefixes and
all its underscores. So i.e. vdo_use_deduplication=1 and
deduplication=1 are equivalent. To change the option for an
already existing VDOPoolLV use lvchange(8) command. However not
all option can be changed. Only compression and deduplication
options can be also changed for an active VDO LV. Lowest priority
options are specified with configuration file, then with
--vdosettings and highest are explicit option --compression and
--deduplication.
Example
# lvcreate --vdo -L10G --vdosettings 'ack_threads=1 hash_zone_threads=2' vg/vdopool0
# lvchange --vdosettings 'bio_threads=2 deduplication=1' vg/vdopool0
6. Checking the usage of VDOPoolLV
To quickly check how much data on a VDOPoolLV is already consumed,
use lvs(8). The Data% field reports how much data is occupied in
the content of the virtual data for the VDOLV and how much space
is already consumed with all the data and metadata blocks in the
VDOPoolLV. For a detailed description, use the vdostats(8)
command.
Note: vdostats(8) currently understands only /dev/mapper device
names.
Example
# lvcreate --type vdo -L10G -V20G -n vdo0 vg/vdopool0
# mkfs.ext4 -E nodiscard /dev/vg/vdo0
# lvs -a vg
LV VG Attr LSize Pool Origin Data%
vdo0 vg vwi-a-v--- 20.00g vdopool0 0.01
vdopool0 vg dwi-ao---- 10.00g 30.16
[vdopool0_vdata] vg Dwi-ao---- 10.00g
# vdostats --all /dev/mapper/vg-vdopool0-vpool
/dev/mapper/vg-vdopool0 :
version : 30
release version : 133524
data blocks used : 79
...
7. Extending the VDOPoolLV size
You can add more space to hold VDO data and metadata by extending
the VDODataLV using the commands lvresize(8) and lvextend(8). The
extension needs to add at least one new VDO slab. You can
configure the slab size with the allocation/vdo_slab_size_mb
setting.
You can also enable automatic size extension of a monitored
VDOPoolLV with the activation/vdo_pool_autoextend_percent and
activation/vdo_pool_autoextend_threshold settings.
Note: You cannot reduce the size of a VDOPoolLV.
lvextend -L+AddingSize VG/VDOPoolLV
Example
# lvextend -L+50G vg/vdopool0
# lvresize -L300G vg/vdopool1
8. Extending or reducing the VDOLV size
You can extend or reduce a virtual VDO LV as a standard LV with
the lvresize(8), lvextend(8), and lvreduce(8) commands.
Note: The reduction needs to process TRIM for reduced disk area to
unmap used data blocks from the VDOPoolLV, which might take a long
time.
lvextend -L+AddingSize VG/VDOLV
lvreduce -L-ReducingSize VG/VDOLV
Example
# lvextend -L+50G vg/vdo0
# lvreduce -L-50G vg/vdo1
# lvresize -L200G vg/vdo2
9. Component activation of a VDODataLV
You can activate a VDODataLV separately as a component LV for
examination purposes. The activation of the VDODataLV activates
the data LV in read-only mode, and the data LV cannot be modified.
If the VDODataLV is active as a component, any upper LV using this
volume CANNOT be activated. You have to deactivate the VDODataLV
first to continue to use the VDOPoolLV.
Example
# lvchange -ay vg/vpool0_vdata
# lvchange -an vg/vpool0_vdata
1. Stacking VDO
You can convert or stack a VDOPooLV with these currently supported
volume types: linear, stripe, raid and cache with cachepool.
1. Using multiple volumes using same VDOPoolLV
You can convert existing VDO LV into a thin volume. After this
conversion you can create a thin snapshot or you can add more thin
volumes with thin-pool named after original LV name LV_tpool0.
See lvmthin(7) for more details.
Example
# lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vdopool
# lvconvert --type thin vg/vdo1
# lvcreate -V20 vg/vdo1_tpool0
2. VDOPoolLV on top of raid
Using a raid type LV for a VDODataLV.
Example
# lvcreate --type raid1 -L 5G -n vdopool vg
# lvconvert --type vdo-pool -V 10G vg/vdopool
3. Caching a VDOPoolLV
VDOPoolLV (accepts also VDODataLV volume name) caching provides a
mechanism to accelerate reads and writes of already compressed and
deduplicated data blocks together with VDO metadata.
Example
# lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vdopool
# lvcreate --type cache-pool -L 1G -n cachepool vg
# lvconvert --cache --cachepool vg/cachepool vg/vdopool
# lvconvert --uncache vg/vdopool
4. Caching a VDOLV
VDO LV cache allow you to 'cache' a device for better performance
before it hits the processing of the VDO Pool LV layer.
Example
# lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vdopool
# lvcreate --type cache-pool -L 1G -n cachepool vg
# lvconvert --cache --cachepool vg/cachepool vg/vdo1
# lvconvert --uncache vg/vdo1
5. Usage of Discard/TRIM with a VDOLV
You can discard data on a VDO LV and reduce used blocks on a
VDOPoolLV. However, the current performance of discard operations
is still not optimal and takes a considerable amount of time and
CPU. Unless you really need it, you should avoid using discard.
When a block device is going to be rewritten, its blocks will be
automatically reused for new data. Discard is useful in
situations when user knows that the given portion of a VDO LV is
not going to be used and the discarded space can be used for block
provisioning in other regions of the VDO LV. For the same reason,
you should avoid using mkfs with discard for a freshly created VDO
LV to save a lot of time that this operation would take otherwise
as device is already expected to be empty.
6. Memory usage
The VDO target requires 38 MiB of RAM and several variable
amounts:
• 1.15 MiB of RAM for each 1 MiB of configured block map cache
size. The block map cache requires a minimum of 150 MiB RAM.
• 1.6 MiB of RAM for each 1 TiB of logical space.
• 268 MiB of RAM for each 1 TiB of physical storage managed by the
volume.
UDS requires a minimum of 250 MiB of RAM, which is also the
default amount that deduplication uses.
The memory required for the UDS index is determined by the index
type and the required size of the deduplication window and is
controlled by the allocation/vdo_use_sparse_index setting.
With enabled UDS sparse indexing, it relies on the temporal
locality of data and attempts to retain only the most relevant
index entries in memory and can maintain a deduplication window
that is ten times larger than with dense while using the same
amount of memory.
Although the sparse index provides the greatest coverage, the
dense index provides more deduplication advice. For most
workloads, given the same amount of memory, the difference in
deduplication rates between dense and sparse indexes is
negligible.
A dense index with 1 GiB of RAM maintains a 1 TiB deduplication
window, while a sparse index with 1 GiB of RAM maintains a 10 TiB
deduplication window. In general, 1 GiB is sufficient for 4 TiB
of physical space with a dense index and 40 TiB with a sparse
index.
7. Storage space requirements
You can configure a VDOPoolLV to use up to 256 TiB of physical
storage. Only a certain part of the physical storage is usable to
store data. This section provides the calculations to determine
the usable size of a VDO-managed volume.
The VDO target requires storage for two types of VDO metadata and
for the UDS index:
• The first type of VDO metadata uses approximately 1 MiB for each
4 GiB of physical storage plus an additional 1 MiB per slab.
• The second type of VDO metadata consumes approximately 1.25 MiB
for each 1 GiB of logical storage, rounded up to the nearest
slab.
• The amount of storage required for the UDS index depends on the
type of index and the amount of RAM allocated to the index. For
each 1 GiB of RAM, a dense UDS index uses 17 GiB of storage and
a sparse UDS index will use 170 GiB of storage.
lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
lvchange(8), lvextend(8), lvreduce(8), lvresize(8), lvremove(8),
lvs(8),
lvmthin(7), vdoformat(8), vdostats(8),
mkfs(8)
This page is part of the lvm2 (Logical Volume Manager 2) project.
Information about the project can be found at
⟨http://www.sourceware.org/lvm2/⟩. If you have a bug report for
this manual page, see ⟨https://github.com/lvmteam/lvm2/issues⟩.
This page was obtained from the project's upstream Git repository
⟨git://sourceware.org/git/lvm2.git⟩ on 2025-08-11. (At that time,
the date of the most recent commit that was found in the
repository was 2025-08-08.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Red Hat, Inc. LVM TOOLS 2.03.35(2)-git (2025-07-30) LVMVDO(7)
Pages that refer to this page: lvchange(8), lvconvert(8), lvcreate(8), lvdisplay(8), lvextend(8), lvm(8), lvmconfig(8), lvmdevices(8), lvmdiskscan(8), lvm-fullreport(8), lvm-lvpoll(8), lvreduce(8), lvremove(8), lvrename(8), lvresize(8), lvs(8), lvscan(8), pvchange(8), pvck(8), pvcreate(8), pvdisplay(8), pvmove(8), pvremove(8), pvresize(8), pvs(8), pvscan(8), vgcfgbackup(8), vgcfgrestore(8), vgchange(8), vgck(8), vgconvert(8), vgcreate(8), vgdisplay(8), vgexport(8), vgextend(8), vgimport(8), vgimportclone(8), vgimportdevices(8), vgmerge(8), vgmknodes(8), vgreduce(8), vgremove(8), vgrename(8), vgs(8), vgscan(8), vgsplit(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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