1LVMVDO(7) LVMVDO(7)
2
6 lvmvdo — Support for Virtual Data Optimizer in LVM
7
9 VDO is software that provides inline block-level deduplication, com‐
10 pression, and thin provisioning capabilities for primary storage.
11 Deduplication is a technique for reducing the consumption of storage
13 resources by eliminating multiple copies of duplicate blocks. Compres‐
14 sion takes the individual unique blocks and shrinks them. These reduced
15 blocks are then efficiently packed together into physical blocks. Thin
16 provisioning manages the mapping from logical blocks presented by VDO
17 to where the data has actually been physically stored, and also elimi‐
18 nates any blocks of all zeroes.
19 With deduplication, instead of writing the same data more than once,
21 VDO detects and records each duplicate block as a reference to the
22 original block. VDO maintains a mapping from Logical Block Addresses
23 (LBA) (used by the storage layer above VDO) to physical block addresses
24 (used by the storage layer under VDO). After deduplication, multiple
25 logical block addresses may be mapped to the same physical block ad‐
26 dress; these are called shared blocks and are reference-counted by the
27 software.
28 With compression, VDO compresses multiple blocks (or shared blocks)
30 with the fast LZ4 algorithm, and bins them together where possible so
31 that multiple compressed blocks fit within a 4 KB block on the underly‐
32 ing storage. Mapping from LBA is to a physical block address and index
33 within it for the desired compressed data. All compressed blocks are
34 individually reference counted for correctness.
35 Block sharing and block compression are invisible to applications using
37 the storage, which read and write blocks as they would if VDO were not
38 present. When a shared block is overwritten, a new physical block is
39 allocated for storing the new block data to ensure that other logical
40 block addresses that are mapped to the shared physical block are not
41 modified.
42 To use VDO with lvm(8), you must install the standard VDO user-space
44 tools vdoformat(8) and the currently non-standard kernel VDO module
45 "kvdo".
46 The "kvdo" module implements fine-grained storage virtualization, thin
48 provisioning, block sharing, and compression. The "uds" module pro‐
49 vides memory-efficient duplicate identification. The user-space tools
50 include vdostats(8) for extracting statistics from VDO volumes.
51
53 VDODataLV
54 VDO data LV
55 A large hidden LV with the _vdata suffix. It is created in a VG
56 used by the VDO kernel target to store all data and metadata
57 blocks.
58 VDOPoolLV
60 VDO pool LV
61 A pool for virtual VDOLV(s), which are the size of used VDO‐
62 DataLV.
63 Only a single VDOLV is currently supported.
64 VDOLV
66 VDO LV
67 Created from VDOPoolLV.
68 Appears blank after creation.
69
71 The primary methods for using VDO with lvm2:
72 1. Create a VDOPoolLV and a VDOLV
74 Create a VDOPoolLV that will hold VDO data, and a virtual size VDOLV
75 that the user can use. If you do not specify the virtual size, then the
76 VDOLV is created with the maximum size that always fits into data vol‐
77 ume even if no deduplication or compression can happen (i.e. it can
78 hold the incompressible content of /dev/urandom). If you do not spec‐
79 ify the name of VDOPoolLV, it is taken from the sequence of vpool0,
80 vpool1 ...
81 Note: The performance of TRIM/Discard operations is slow for large vol‐
83 umes of VDO type. Please try to avoid sending discard requests unless
84 necessary because it might take considerable amount of time to finish
85 the discard operation.
86 lvcreate --type vdo -n VDOLV -L DataSize -V LargeVirtualSize VG/VDOPoolLV
88 lvcreate --vdo -L DataSize VG
89 Example
91 # lvcreate --type vdo -n vdo0 -L 10G -V 100G vg/vdopool0
92 # mkfs.ext4 -E nodiscard /dev/vg/vdo0
93 2. Convert an existing LV into VDOPoolLV
95 Convert an already created or existing LV into a VDOPoolLV, which is a
96 volume that can hold data and metadata. You will be prompted to con‐
97 firm such conversion because it IRREVERSIBLY DESTROYS the content of
98 such volume and the volume is immediately formatted by vdoformat(8) as
99 a VDO pool data volume. You can specify the virtual size of the VDOLV
100 associated with this VDOPoolLV. If you do not specify the virtual
101 size, it will be set to the maximum size that can keep 100% incompress‐
102 ible data there.
103 lvconvert --type vdo-pool -n VDOLV -V VirtualSize VG/VDOPoolLV
105 lvconvert --vdopool VG/VDOPoolLV
106 Example
108 # lvconvert --type vdo-pool -n vdo0 -V10G vg/ExistingLV
109 3. Change the default settings used for creating a VDOPoolLV
111 VDO allows to set a large variety of options. Lots of these settings
112 can be specified in lvm.conf or profile settings. You can prepare a
113 number of different profiles in the /etc/lvm/profile directory and just
114 specify the profile file name. Check the output of lvmconfig --type
115 full for a detailed description of all individual VDO settings.
116 Example
118 # cat <<EOF > /etc/lvm/profile/vdo_create.profile
119 allocation {
120 vdo_use_compression=1
121 vdo_use_deduplication=1
122 vdo_use_metadata_hints=1
123 vdo_minimum_io_size=4096
124 vdo_block_map_cache_size_mb=128
125 vdo_block_map_period=16380
126 vdo_check_point_frequency=0
127 vdo_use_sparse_index=0
128 vdo_index_memory_size_mb=256
129 vdo_slab_size_mb=2048
130 vdo_ack_threads=1
131 vdo_bio_threads=1
132 vdo_bio_rotation=64
133 vdo_cpu_threads=2
134 vdo_hash_zone_threads=1
135 vdo_logical_threads=1
136 vdo_physical_threads=1
137 vdo_write_policy="auto"
138 vdo_max_discard=1
139 }
140 EOF
141 # lvcreate --vdo -L10G --metadataprofile vdo_create vg/vdopool0
143 # lvcreate --vdo -L10G --config 'allocation/vdo_cpu_threads=4' vg/vdopool1
144 4. Change the compression and deduplication of a VDOPoolLV
146 Disable or enable the compression and deduplication for VDOPoolLV (the
147 volume that maintains all VDO LV(s) associated with it).
148 lvchange --compression [y|n] --deduplication [y|n] VG/VDOPoolLV
150 Example
152 # lvchange --compression n vg/vdopool0
153 # lvchange --deduplication y vg/vdopool1
154 5. Checking the usage of VDOPoolLV
156 To quickly check how much data on a VDOPoolLV is already consumed, use
157 lvs(8). The Data% field reports how much data is occupied in the con‐
158 tent of the virtual data for the VDOLV and how much space is already
159 consumed with all the data and metadata blocks in the VDOPoolLV. For a
160 detailed description, use the vdostats(8) command.
161 Note: vdostats(8) currently understands only /dev/mapper device names.
163 Example
165 # lvcreate --type vdo -L10G -V20G -n vdo0 vg/vdopool0
166 # mkfs.ext4 -E nodiscard /dev/vg/vdo0
167 # lvs -a vg
168 LV VG Attr LSize Pool Origin Data%
170 vdo0 vg vwi-a-v--- 20.00g vdopool0 0.01
171 vdopool0 vg dwi-ao---- 10.00g 30.16
172 [vdopool0_vdata] vg Dwi-ao---- 10.00g
173 # vdostats --all /dev/mapper/vg-vdopool0-vpool
175 /dev/mapper/vg-vdopool0 :
176 version : 30
177 release version : 133524
178 data blocks used : 79
179 ...
180 6. Extending the VDOPoolLV size
182 You can add more space to hold VDO data and metadata by extending the
183 VDODataLV using the commands lvresize(8) and lvextend(8). The exten‐
184 sion needs to add at least one new VDO slab. You can configure the slab
185 size with the allocation/vdo_slab_size_mb setting.
186 You can also enable automatic size extension of a monitored VDOPoolLV
188 with the activation/vdo_pool_autoextend_percent and activa‐
189 tion/vdo_pool_autoextend_threshold settings.
190 Note: You cannot reduce the size of a VDOPoolLV.
192 Note: You cannot change the size of a cached VDOPoolLV.
194 lvextend -L+AddingSize VG/VDOPoolLV
196 Example
198 # lvextend -L+50G vg/vdopool0
199 # lvresize -L300G vg/vdopool1
200 7. Extending or reducing the VDOLV size
202 You can extend or reduce a virtual VDO LV as a standard LV with the
203 lvresize(8), lvextend(8), and lvreduce(8) commands.
204 Note: The reduction needs to process TRIM for reduced disk area to un‐
206 map used data blocks from the VDOPoolLV, which might take a long time.
207 lvextend -L+AddingSize VG/VDOLV
209 lvreduce -L-ReducingSize VG/VDOLV
210 Example
212 # lvextend -L+50G vg/vdo0
213 # lvreduce -L-50G vg/vdo1
214 # lvresize -L200G vg/vdo2
215 8. Component activation of a VDODataLV
217 You can activate a VDODataLV separately as a component LV for examina‐
218 tion purposes. The activation of the VDODataLV activates the data LV in
219 read-only mode, and the data LV cannot be modified. If the VDODataLV
220 is active as a component, any upper LV using this volume CANNOT be ac‐
221 tivated. You have to deactivate the VDODataLV first to continue to use
222 the VDOPoolLV.
223 Example
225 # lvchange -ay vg/vpool0_vdata
226 # lvchange -an vg/vpool0_vdata
227
229 1. Stacking VDO
230 You can convert or stack a VDOPooLV with these currently supported vol‐
231 ume types: linear, stripe, raid, and cache with cachepool.
232 2. VDOPoolLV on top of raid
234 Using a raid type LV for a VDODataLV.
235 Example
237 # lvcreate --type raid1 -L 5G -n vdopool vg
238 # lvconvert --type vdo-pool -V 10G vg/vdopool
239 3. Caching a VDODataLV or a VDOPoolLV
241 VDODataLV (accepts also VDOPoolLV) caching provides a mechanism to ac‐
242 celerate reads and writes of already compressed and deduplicated data
243 blocks together with VDO metadata.
244 A cached VDO data LV cannot be currently resized. Also, the threshold
246 based automatic resize will not work.
247 Example
249 # lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vdopool
250 # lvcreate --type cache-pool -L 1G -n cachepool vg
251 # lvconvert --cache --cachepool vg/cachepool vg/vdopool
252 # lvconvert --uncache vg/vdopool
253 4. Caching a VDOLV
255 VDO LV cache allow you to 'cache' a device for better performance be‐
256 fore it hits the processing of the VDO Pool LV layer.
257 Example
259 # lvcreate --type vdo -L 5G -V 10G -n vdo1 vg/vdopool
260 # lvcreate --type cache-pool -L 1G -n cachepool vg
261 # lvconvert --cache --cachepool vg/cachepool vg/vdo1
262 # lvconvert --uncache vg/vdo1
263 5. Usage of Discard/TRIM with a VDOLV
265 You can discard data on a VDO LV and reduce used blocks on a VDOPoolLV.
266 However, the current performance of discard operations is still not op‐
267 timal and takes a considerable amount of time and CPU. Unless you re‐
268 ally need it, you should avoid using discard.
269 When a block device is going to be rewritten, its blocks will be auto‐
271 matically reused for new data. Discard is useful in situations when
272 user knows that the given portion of a VDO LV is not going to be used
273 and the discarded space can be used for block provisioning in other re‐
274 gions of the VDO LV. For the same reason, you should avoid using mkfs
275 with discard for a freshly created VDO LV to save a lot of time that
276 this operation would take otherwise as device is already expected to be
277 empty.
278 6. Memory usage
280 The VDO target requires 370 MiB of RAM plus an additional 268 MiB per
281 each 1 TiB of physical storage managed by the volume.
282 UDS requires a minimum of 250 MiB of RAM, which is also the default
284 amount that deduplication uses.
285 The memory required for the UDS index is determined by the index type
287 and the required size of the deduplication window and is controlled by
288 the allocation/vdo_use_sparse_index setting.
289 With enabled UDS sparse indexing, it relies on the temporal locality of
291 data and attempts to retain only the most relevant index entries in
292 memory and can maintain a deduplication window that is ten times larger
293 than with dense while using the same amount of memory.
294 Although the sparse index provides the greatest coverage, the dense in‐
296 dex provides more deduplication advice. For most workloads, given the
297 same amount of memory, the difference in deduplication rates between
298 dense and sparse indexes is negligible.
299 A dense index with 1 GiB of RAM maintains a 1 TiB deduplication window,
301 while a sparse index with 1 GiB of RAM maintains a 10 TiB deduplication
302 window. In general, 1 GiB is sufficient for 4 TiB of physical space
303 with a dense index and 40 TiB with a sparse index.
304 7. Storage space requirements
306 You can configure a VDOPoolLV to use up to 256 TiB of physical storage.
307 Only a certain part of the physical storage is usable to store data.
308 This section provides the calculations to determine the usable size of
309 a VDO-managed volume.
310 The VDO target requires storage for two types of VDO metadata and for
312 the UDS index:
313 • The first type of VDO metadata uses approximately 1 MiB for each
315 4 GiB of physical storage plus an additional 1 MiB per slab.
316 • The second type of VDO metadata consumes approximately 1.25 MiB
318 for each 1 GiB of logical storage, rounded up to the nearest
319 slab.
320 • The amount of storage required for the UDS index depends on the
322 type of index and the amount of RAM allocated to the index. For
323 each 1 GiB of RAM, a dense UDS index uses 17 GiB of storage and
324 a sparse UDS index will use 170 GiB of storage.
325
328 lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
329 lvchange(8), lvextend(8), lvreduce(8), lvresize(8), lvremove(8),
330 lvs(8), vdo(8), vdoformat(8), vdostats(8), mkfs(8)
331Red Hat, Inc LVM TOOLS 2.03.11(2) (2021-01-08) LVMVDO(7)