Ubuntu Manpage: lvmvdo — EXPERIMENTAL LVM Virtual Data Optimizer support

Provided by: lvm2_2.03.07-1ubuntu1_amd64

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 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 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 compressed with the fast LZ4 algorithm,
and binned 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.

For usage of VDO with lvm(8) standard VDO userspace tools vdoformat(8) and currently non-standard kernel
VDO module "kvdo" needs to be installed 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 unless 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 vdoformat(8) as VDO pool data
volume. User can specify virtual size of associated VDOLV with this VDOPoolLV. When the virtual size is
not specified, 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 virtual 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 extension 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 lvresize(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 modified. 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

NAME

DESCRIPTION

VDO Terms

VDO Usage

VDO Topics

SEE ALSO