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1 .. SPDX-License-Identifier: GPL-2.0-only
3 dm-vdo
6 The dm-vdo (virtual data optimizer) device mapper target provides
7 block-level deduplication, compression, and thin provisioning. As a device
20 https://github.com/dm-vdo/vdo/
23 next time it is started. In cases where it encountered an unrecoverable
25 enter or come up in read-only mode. Because read-only mode is indicative of
26 data-loss, a positive action must be taken to bring vdo out of read-only
28 prepare a read-only vdo to exit read-only mode. After running this tool,
29 the vdo target will rebuild its metadata the next time it is
34 inspect a vdo target's on-disk metadata. Fortunately, these tools are
35 rarely needed except by dm-vdo developers.
46 https://github.com/dm-vdo/vdoestimator/
52 ----------
57 <storage device size> <minimum I/O size> <block map cache size>
77 of 4096-byte blocks. Must match the current size of the vdo
85 block map cache size:
86 The size of the block map cache, as a number of 4096-byte
88 If the logical thread count is non-zero, the cache size
92 The speed with which the block map cache writes out
100 --------------------
110 values are non-zero, all of them must be non-zero.
127 switching to the next thread. The value must be greater
131 The number of threads used to do CPU-intensive work, such
154 The maximum size of discard bio accepted, in 4096-byte
156 into 4096-byte blocks, and processed up to 2048 at a time.
159 4096-byte blocks in a single bio, and are limited to 1500
174 -------------------
176 A modified table may be loaded into a running, non-suspended vdo volume.
177 The modifications will take effect when the device is next resumed. The
185 least 32832 4096-byte blocks if at all, and must not exceed the size of the
193 Start a previously-formatted vdo volume with 1 GB logical space and 1 GB
194 physical space, storing to /dev/dm-1 which has more than 1 GB of space.
198 dmsetup create vdo0 --table \
199 "0 2097152 vdo V4 /dev/dm-1 262144 4096 32768 16380"
205 dmsetup reload vdo0 --table \
206 "0 8388608 vdo V4 /dev/dm-1 262144 4096 32768 16380"
213 dmsetup reload vdo0 --table \
214 "0 8388608 vdo V4 /dev/dm-1 524288 4096 32768 16380"
221 dmsetup reload vdo0 --table \
222 "0 10485760 vdo V4 /dev/dm-1 786432 4096 32768 16380 maxDiscard 8"
236 dmsetup create vdo1 --table \
237 "0 10485760 vdo V4 /dev/dm-1 786432 512 65550 5000 hash 1 logical 3 physical 2"
240 --------
245 dmsetup message <target-name> 0 <message-name> <message-parameters>
267 vdo: Most of the structures managing on-disk data
273 dump-on-shutdown:
274 Perform a default dump next time vdo shuts down.
278 ------
292 'read-only' (an error has occurred that forces the vdo
297 values may be 'recovering' or '-' which indicates not
324 - 1.15 MB of RAM for each 1 MB of configured block map cache size. The
325 block map cache requires a minimum of 150 MB.
326 - 1.6 MB of RAM for each 1 TB of logical space.
327 - 268 MB of RAM for each 1 TB of physical storage managed by the volume.
342 Run-time Usage
345 When using dm-vdo, it is important to be aware of the ways in which its
348 - There is no guarantee that over-writes of existing blocks will succeed.
349 Because the underlying storage may be multiply referenced, over-writing
353 - When blocks are no longer in use, sending a discard request for those
360 - Assuming the underlying storage properly implements flush requests, vdo
364 - Each write to a vdo target entails a significant amount of processing.
380 The most important value to adjust is the block map cache size. In order to
383 Performance will suffer when the working set does not fit in the cache. By
384 default, a vdo allocates 128 MB of metadata cache in RAM to support
404 bios have CPU-heavy callbacks.
411 threads are comparison of 4096-byte data blocks. In most cases, a single