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366 lines
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366 lines
10 KiB
Plaintext
.TH "LVMVDO" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
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.SH NAME
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lvmvdo \(em LVM Virtual Data Optimizer support
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.SH DESCRIPTION
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VDO (which includes kvdo and vdo) is software that provides inline
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block-level deduplication, compression, and thin provisioning capabilities
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for primary storage.
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Deduplication is a technique for reducing the consumption of storage
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resources by eliminating multiple copies of duplicate blocks. Compression
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takes the individual unique blocks and shrinks them with coding
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algorithms; these reduced blocks are then efficiently packed together into
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physical blocks. Thin provisioning manages the mapping from LBAs presented
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by VDO to where the data has actually been stored, and also eliminates any
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blocks of all zeroes.
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With deduplication, instead of writing the same data more than once each
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duplicate block is detected and recorded as a reference to the original
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block. VDO maintains a mapping from logical block addresses (used by the
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storage layer above VDO) to physical block addresses (used by the storage
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layer under VDO). After deduplication, multiple logical block addresses
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may be mapped to the same physical block address; these are called shared
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blocks and are reference-counted by the software.
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With VDO's compression, multiple blocks (or shared blocks) are compressed
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with the fast LZ4 algorithm, and binned together where possible so that
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multiple compressed blocks fit within a 4 KB block on the underlying
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storage. Mapping from LBA is to a physical block address and index within
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it for the desired compressed data. All compressed blocks are individually
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reference counted for correctness.
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Block sharing and block compression are invisible to applications using
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the storage, which read and write blocks as they would if VDO were not
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present. When a shared block is overwritten, a new physical block is
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allocated for storing the new block data to ensure that other logical
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block addresses that are mapped to the shared physical block are not
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modified.
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For usage of VDO with \fBlvm\fP(8) standard VDO userspace tools
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\fBvdoformat\fP(8) and currently non-standard kernel VDO module
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"\fIkvdo\fP" needs to be installed on the system.
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The "\fIkvdo\fP" module implements fine-grained storage virtualization,
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thin provisioning, block sharing, and compression;
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the "\fIuds\fP" module provides memory-efficient duplicate
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identification. The userspace tools include \fBvdostats\fP(8)
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for extracting statistics from those volumes.
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.SH VDO Terms
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.TP
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VDODataLV
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.br
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VDO data LV
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.br
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large hidden LV with suffix _vdata created in a VG.
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.br
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used by VDO target to store all data and metadata blocks.
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.TP
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VDOPoolLV
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.br
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VDO pool LV
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.br
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maintains virtual for LV(s) stored in attached VDO data LV
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and it has same size.
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.br
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contains VDOLV(s) (currently supports only a single VDOLV).
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.TP
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VDOLV
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.br
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VDO LV
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.br
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created from VDOPoolLV
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.br
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appears blank after creation
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.SH VDO Usage
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The primary methods for using VDO with lvm2:
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.SS 1. Create VDOPoolLV with VDOLV
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Create a VDOPoolLV that will hold VDO data together with
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virtual size VDOLV, that user can use. When the virtual size
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is not specified, then such LV is created with maximum size that
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always fits into data volume even if there cannot happen any
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deduplication and compression
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(i.e. it can hold uncompressible content of /dev/urandom).
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When the name of VDOPoolLV is not specified, it is taken from
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the sequence of vpool0, vpool1 ...
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Note: As the performance of TRIM/Discard operation is slow for large
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volumes of VDO type, please try to avoid sending discard requests unless
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necessary as it may take considerable amount of time to finish discard
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operation.
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.nf
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.B lvcreate --type vdo -n VDOLV -L DataSize -V LargeVirtualSize VG/VDOPoolLV
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.B lvcreate --vdo -L DataSize VG
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.fi
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.I Example
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.br
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.nf
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# lvcreate --type vdo -n vdo0 -L 10G -V 100G vg/vdopool0
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# mkfs.ext4 -E nodiscard /dev/vg/vdo0
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.fi
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.SS 2. Create VDOPoolLV from conversion of an existing LV into VDODataLV
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Convert an already created/existing LV into a volume that can hold
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VDO data and metadata (a volume reference by VDOPoolLV).
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User will be prompted to confirm such conversion as it is \fBIRREVERSIBLY
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DESTROYING\fP content of such volume, as it's being immediately
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formatted by \fBvdoformat\fP(8) as VDO pool data volume. User can
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specify virtual size of associated VDOLV with this VDOPoolLV.
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When the virtual size is not specified, it will be set to the maximum size
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that can keep 100% uncompressible data there.
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.nf
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.B lvconvert --type vdo-pool -n VDOLV -V VirtualSize VG/VDOPoolLV
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.B lvconvert --vdopool VG/VDOPoolLV
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.fi
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.I Example
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.br
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.nf
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# lvconvert --type vdo-pool -n vdo0 -V10G vg/existinglv
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.fi
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.SS 3. Change default settings used for creating VDOPoolLV
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VDO allows to set large variety of options. Lots of these settings
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can be specified by lvm.conf or profile settings. User can prepare
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number of different profiles in #DEFAULT_SYS_DIR#/profile directory
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and just specify profile file name.
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Check output of \fBlvmconfig --type full\fP for detailed description
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of all individual vdo settings.
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.I Example
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.br
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.nf
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# cat <<EOF > #DEFAULT_SYS_DIR#/profile/vdo_create.profile
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allocation {
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vdo_use_compression=1
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vdo_use_deduplication=1
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vdo_use_metadata_hints=1
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vdo_minimum_io_size=4096
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vdo_block_map_cache_size_mb=128
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vdo_block_map_period=16380
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vdo_check_point_frequency=0
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vdo_use_sparse_index=0
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vdo_index_memory_size_mb=256
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vdo_slab_size_mb=2048
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vdo_ack_threads=1
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vdo_bio_threads=1
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vdo_bio_rotation=64
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vdo_cpu_threads=2
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vdo_hash_zone_threads=1
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vdo_logical_threads=1
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vdo_physical_threads=1
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vdo_write_policy="auto"
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vdo_max_discard=1
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}
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EOF
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# lvcreate --vdo -L10G --metadataprofile vdo_create vg/vdopool0
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# lvcreate --vdo -L10G --config 'allocation/vdo_cpu_threads=4' vg/vdopool1
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.fi
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.SS 4. Change compression and deduplication of VDOPoolLV
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Disable or enable compression and deduplication for VDO pool LV
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(the volume that maintains all VDO LV(s) associated with it).
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.nf
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.B lvchange --compression [y|n] --deduplication [y|n] VG/VDOPoolLV
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.fi
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.I Example
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.br
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.nf
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# lvchange --compression n vg/vdpool0
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# lvchange --deduplication y vg/vdpool1
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.fi
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.SS 5. Checking usage of VDOPoolLV
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To quickly check how much data of VDOPoolLV are already consumed
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use \fBlvs\fP(8). Field Data% will report how much data occupies
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content of virtual data for VDOLV and how much space is already
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consumed with all the data and metadata blocks in VDOPoolLV.
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For a detailed description use \fBvdostats\fP(8) command.
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Note: \fBvdostats\fP(8) currently understands only /dev/mapper device names.
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.I Example
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.br
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.nf
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# lvcreate --type vdo -L10G -V20G -n vdo0 vg/vdopool0
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# mkfs.ext4 -E nodiscard /dev/vg/vdo0
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# lvs -a vg
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LV VG Attr LSize Pool Origin Data%
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vdo0 vg vwi-a-v--- 20.00g vdopool0 0.01
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vdopool0 vg dwi-ao---- 10.00g 30.16
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[vdopool0_vdata] vg Dwi-ao---- 10.00g
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# vdostats --all /dev/mapper/vg-vdopool0-vpool
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/dev/mapper/vg-vdopool0 :
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version : 30
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release version : 133524
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data blocks used : 79
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...
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.fi
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.SS 6. Extending VDOPoolLV size
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Adding more space to hold VDO data and metadata can be made via
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extension of VDODataLV with commands
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\fBlvresize\fP(8), \fBlvextend\fP(8).
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Note: Size of VDOPoolLV cannot be reduced.
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Note: Size of cached VDOPoolLV cannot be changed.
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.nf
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.B lvextend -L+AddingSize VG/VDOPoolLV
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.fi
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.I Example
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.br
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.nf
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# lvextend -L+50G vg/vdopool0
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# lvresize -L300G vg/vdopool1
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.fi
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.SS 7. Extending or reducing VDOLV size
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VDO LV can be extended or reduced as standard LV with commands
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\fBlvresize\fP(8), \fBlvextend\fP(8), \fBlvreduce\fP(8).
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Note: Reduction needs to process TRIM for reduced disk area
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to unmap used data blocks from VDOPoolLV and it may take
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a long time.
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.nf
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.B lvextend -L+AddingSize VG/VDOLV
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.B lvreduce -L-ReducingSize VG/VDOLV
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.fi
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.I Example
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.br
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.nf
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# lvextend -L+50G vg/vdo0
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# lvreduce -L-50G vg/vdo1
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# lvresize -L200G vg/vdo2
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.fi
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.SS 8. Component activation of VDODataLV
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VDODataLV can be activated separately as component LV for examination
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purposes. It activates data LV in read-only mode and cannot be modified.
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If the VDODataLV is active as component, any upper LV using this volume CANNOT
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be activated. User has to deactivate VDODataLV first to continue to use VDOPoolLV.
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.I Example
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.br
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.nf
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# lvchange -ay vg/vpool0_vdata
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# lvchange -an vg/vpool0_vdata
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.fi
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.SH VDO Topics
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.SS 1. Stacking VDO
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User can convert/stack VDO with existing volumes.
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.SS 2. VDO on top of raid
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Using Raid type LV for VDO Data LV.
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.I Example
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.br
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.nf
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# lvcreate --type raid1 -L 5G -n vpool vg
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# lvconvert --type vdo-pool -V 10G vg/vpool
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.fi
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.SS 3. Caching VDODataLV, VDOPoolLV
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VDO Pool LV (accepts also VDOPoolLV) caching provides mechanism
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to accelerate read and write of already compressed and deduplicated
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blocks together with vdo metadata.
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Cached VDO Data LV cannot be currently resized (also automatic
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resize will not work).
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.I Example
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.br
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.nf
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# lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vpool
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# lvcreate --type cache-pool -L 1G -n cpool vg
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# lvconvert --cache --cachepool vg/cpool vg/vpool
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# lvconvert --uncache vg/vpool
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.fi
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.SS 4. Caching VDOLV
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VDO LV cache allow users to 'cache' device for better perfomance before
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it hits processing of VDO Pool LV layer.
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.I Example
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.br
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.nf
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# lvcreate -L 5G -V 10G -n vdo1 vg/vpool
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# lvcreate --type cache-pool -L 1G -n cpool vg
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# lvconvert --cache --cachepool vg/cpool vg/vdo1
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# lvconvert --uncache vg/vdo1
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.fi
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.SS 5. Usage of Discard/TRIM with VDOLV
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User can discard data in VDO LV and reduce used blocks in VDOPoolLV.
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However present performance of discard operation is still not optimal
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and takes considerable amount of time and CPU.
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So unless it's really needed users should avoid usage of discard.
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When block device is going to be rewritten,
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block will be automatically reused for new data.
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Discard is useful in situation, when it is known the given portion of a VDO LV
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is not going to be used and the discarded space can be used for block
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provisioning in other regions of VDO LV.
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For the same reason, user should avoid using mkfs with discard for
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freshly created VDO LV to save a lot of time this operation would
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take otherwise as device after create empty.
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.br
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\&
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.SH SEE ALSO
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.BR lvm (8),
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.BR lvm.conf (5),
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.BR lvmconfig (8),
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.BR lvcreate (8),
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.BR lvconvert (8),
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.BR lvchange (8),
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.BR lvextend (8),
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.BR lvreduce (8),
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.BR lvresize (8),
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.BR lvremove (8),
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.BR lvs (8),
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.BR vdo (8),
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.BR vdoformat (8),
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.BR vdostats (8),
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.BR mkfs (8)
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