lvmvdo(7) — Linux manual page

NAME | DESCRIPTION | VDO TERMS | VDO USAGE | VDO TOPICS | SEE ALSO | COLOPHON

LVMVDO(7)                                                      LVMVDO(7)

NAME         top

       lvmvdo — Support for Virtual Data Optimizer in LVM

DESCRIPTION         top

       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         top

       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         top

       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 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_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.

       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         top

   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 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 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         top

       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)

COLOPHON         top

       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⟩.
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Red Hat, Inc        LVM TOOLS 2.03.12(2) (2021-05-07)          LVMVDO(7)

Pages that refer to this page: lvchange(8)lvconvert(8)lvcreate(8)lvextend(8)lvresize(8)