LVMVDO(7)LVMVDO(7)
NAME
lvmvdo -- EXPERIMENTAL LVM Virtual Data Optimizer support
DESCRIPTION
VDO (which includes kvdo and vdo) is software that provides inline
block-level deduplication, compression, and thin provisioning capabili-
ties for primary storage.
Deduplication is a technique for reducing the consumption of storage
resources by eliminating multiple copies of duplicate blocks. Compres-
sion takes the individual unique blocks and shrinks them with coding
algorithms; these reduced blocks are then efficiently packed together
into physical blocks. Thin provisioning manages the mapping from LBAs
presented by VDO to where the data has actually been stored, and also
eliminates any blocks of all zeroes.
With deduplication, instead of writing the same data more than once
each duplicate block is detected and recorded as a reference to the
original block. VDO maintains a mapping from logical block addresses
(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 VDO's compression, multiple blocks (or shared blocks) are com-
pressed with the fast LZ4 algorithm, and binned together where possible
so that multiple compressed blocks fit within a 4 KB block on the un-
derlying 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.
For usage of VDO with lvm(8) standard VDO userspace tools vdoformat(8)
and currently non-standard kernel VDO module "kvdo" needs to be in-
stalled on the system.
The "kvdo" module implements fine-grained storage virtualization, thin
provisioning, block sharing, and compression; the "uds" module provides
memory-efficient duplicate identification. The userspace tools include
vdostats(8) for extracting statistics from those volumes.
VDO Terms
VDODataLV
VDO data LV
large hidden LV with suffix _vdata created in a VG.
used by VDO target to store all data and metadata blocks.
VDOPoolLV
VDO pool LV
maintains virtual for LV(s) stored in attached VDO data LV and
it has same size.
contains VDOLV(s) (currently supports only a single VDOLV).
VDOLV
VDO LV
created from VDOPoolLV
appears blank after creation
VDO Usage
The primary methods for using VDO with lvm2:
1. Create VDOPoolLV with VDOLV
Create an VDOPoolLV that will holds VDO data together with virtual size
VDOLV, that user can use. When the virtual size is not specified, then
such LV is created with maximum size that always fits into data volume
even if there cannot happen any deduplication and compression (i.e. it
can hold uncompressible content of /dev/urandom). When the name of
VDOPoolLV is not specified, it tales name from sequence of vpool0,
vpool1 ...
Note: As the performance of TRIM/Discard operation is slow for large
volumes of VDO type, please try to avoid sending discard requests un-
less necessary as it may take considerable amount of time to finish
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. Create VDOPoolLV and convert existing LV into VDODataLV
Convert an already created/existing LV into a volume that can hold VDO
data and metadata (a volume reference by VDOPoolLV). User will be
prompted to confirm such conversion as it is IRREVERSIBLY DESTROYING
content of such volume, as it's being immediately formatted by vdofor-
mat(8) as VDO pool data volume. User can specify virtual size of asso-
ciated VDOLV with this VDOPoolLV. When the virtual size is not speci-
fied, it will set to the maximum size that can keep 100% uncompressible
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 default setting used for creating VDOPoolLV
VDO allows to set large variety of option. Lots of these setting can be
specified by lvm.conf or profile settings. User can prepare number of
different profiles and just specify profile file name. Check output of
lvmconfig --type full for detailed description of all individual vdo
settings.
Example
# cat <<EOF > vdo.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_check_point_frequency=0
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.profile vg/vdopool0
# lvcreate --vdo -L10G --config 'allocation/vdo_cpu_threads=4' vg/vdopool1
4. Change compression and deduplication of VDOPoolLV
Disable or enable compression and deduplication for VDO pool LV (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/vdpool0
# lvchange --deduplication y vg/vdpool1
4. Checking usage of VDOPoolLV
To quickly check how much data of VDOPoolLV are already consumed use
lvs(8). Field Data% will report how much data occupies content of vir-
tual data for VDOLV and how much space is already consumed with all the
data and metadata blocks in VDOPoolLV. For a detailed description use
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
/dev/mapper/vg-vdopool0 :
version : 30
release version : 133524
data blocks used : 79
...
4. Extending VDOPoolLV size
Adding more space to hold VDO data and metadata can be made via exten-
sion of VDODataLV with commands lvresize(8), lvextend(8).
Note: Size of VDOPoolLV cannot be reduced.
lvextend -L+AddingSize VG/VDOPoolLV
Example
# lvextend -L+50G vg/vdopool0
# lvresize -L300G vg/vdopool1
4. Extending or reducing VDOLV size
VDO LV can be extended or reduced as standard LV with commands lvre-
size(8), lvextend(8), lvreduce(8).
Note: Reduction needs to process TRIM for reduced disk area to unmap
used data blocks from VDOPoolLV and it may 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
5. Component activation of VDODataLV
VDODataLV can be activated separately as component LV for examination
purposes. It activates data LV in read-only mode and cannot be modi-
fied. If the VDODataLV is active as component, any upper LV using this
volume CANNOT be activated. User has to deactivate VDODataLV first to
continue to use VDOPoolLV.
Example
# lvchange -ay vg/vpool0_vdata
# lvchange -an vg/vpool0_vdata
VDO Topics
1. Stacking VDO
User can convert/stack VDO with existing volumes.
2. VDO on top of raid
Using Raid type LV for VDO Data LV.
Example
# lvcreate --type raid1 -L 5G -n vpool vg
# lvconvert --type vdo-pool -V 10G vg/vpool
3. Caching VDODataLV, VDOPoolLV
Cache VDO Data LV (accepts also VDOPoolLV.
Example
# lvcreate -L 5G -V 10G -n vdo1 vg/vpool
# lvcreate --type cache-pool -L 1G -n cpool vg
# lvconvert --cache --cachepool vg/cpool vg/vpool
# lvconvert --uncache vg/vpool
3. Caching VDOLV
Cache VDO LV.
Example
# lvcreate -L 5G -V 10G -n vdo1 vg/vpool
# lvcreate --type cache-pool -L 1G -n cpool vg
# lvconvert --cache --cachepool vg/cpool vg/vdo1
# lvconvert --uncache vg/vdo1
SEE ALSO
lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
lvchange(8), lvextend(8), lvreduce(8), lvresize(8), lvremove(8),
lvs(8), vdo(8), vdoformat(8), vdostats(8), mkfs(8)
Red Hat, Inc LVM TOOLS 2.03.07(2) (2019-11-30) LVMVDO(7)