Provided by: lvm2_2.03.16-1ubuntu1_amd64 bug


       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

       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 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.

              VDO pool LV
              A pool for virtual VDOLV(s), which are the size of used VDODataLV.
              Only a single VDOLV is currently supported.

              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

       # 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

       # 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

       # 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

       # cat <<EOF > /etc/lvm/profile/vdo_create.profile
       allocation {

       # 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.


       # 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.

       # 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

       Note: You cannot reduce the size of a VDOPoolLV.

       lvextend -L+AddingSize VG/VDOPoolLV

       # 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

       # 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.

       # 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.

   2. VDOPoolLV on top of raid
       Using a raid type LV for a VDODataLV.

       # 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

       # 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.

       # 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

       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),

       vdo(8), vdoformat(8), vdostats(8),