Provided by: lvm2_2.03.11-2.1ubuntu4_amd64 
NAME
lvmvdo — Support for Virtual Data Optimizer in LVM
DESCRIPTION
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.
VDO TERMS
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.
VDO USAGE
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 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 full 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_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_create vg/vdopool0
# lvcreate --vdo -L10G --config 'allocation/vdo_cpu_threads=4' vg/vdopool1
4. 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
5. 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
...
6. 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.
Note: You cannot change the size of a cached VDOPoolLV.
lvextend -L+AddingSize VG/VDOPoolLV
Example
# lvextend -L+50G vg/vdopool0
# lvresize -L300G vg/vdopool1
7. 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
8. 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
VDO TOPICS
1. Stacking VDO
You can convert or stack a VDOPooLV with these currently supported volume types: linear,
stripe, raid, and cache with cachepool.
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 VDODataLV or a VDOPoolLV
VDODataLV (accepts also VDOPoolLV) caching provides a mechanism to accelerate reads and
writes of already compressed and deduplicated data blocks together with VDO metadata.
A cached VDO data LV cannot be currently resized. Also, the threshold based automatic
resize will not work.
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 370 MiB of RAM plus an additional 268 MiB per 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.
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)