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NAME | DESCRIPTION | VDO TERMS | VDO USAGE | VDO TOPICS | SEE ALSO | COLOPHON |
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LVMVDO(7) 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 the currently non-standard kernel
VDO module "kvdo".
The "kvdo" module implements fine-grained storage virtualization,
thin provisioning, block sharing, and compression. The "uds"
module provides memory-efficient duplicate identification. The
user-space tools include vdostats(8) for extracting statistics
from VDO volumes.
VDODataLV
VDO data LV
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
A pool for virtual VDOLV(s), which are the size of used
VDODataLV.
Only a single VDOLV is currently supported.
VDOLV
VDO 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
there.
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 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_use_metadata_hints=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_write_policy="auto"
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_metadata_hints=1 and
metadatahints=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 expliction 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 orignal LV name
LV_tpool0.
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),
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-11.) 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 2.03.25(2)-git (2024-05-16) 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 2024-06-26 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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