1 =================
2 Writecache target
3 =================
4
5 The writecache target caches writes on persist
6 doesn't cache reads because reads are supposed
7 in normal RAM.
8
9 When the device is constructed, the first sect
10 first sector should contain valid superblock f
11
12 Constructor parameters:
13
14 1. type of the cache device - "p" or "s"
15 - p - persistent memory
16 - s - SSD
17 2. the underlying device that will be cached
18 3. the cache device
19 4. block size (4096 is recommended; the maximu
20 size)
21 5. the number of optional parameters (the para
22 count as two)
23
24 start_sector n (default: 0)
25 offset from the start of cache
26 high_watermark n (default: 50)
27 start writeback when the numbe
28 watermark
29 low_watermark x (default: 45)
30 stop writeback when the number
31 this watermark
32 writeback_jobs n (default: unli
33 limit the number of blocks tha
34 writeback. Setting this value
35 throughput, but it may improve
36 autocommit_blocks n (default: 64 f
37 when the application writes th
38 issuing the FLUSH request, the
39 committed
40 autocommit_time ms (default: 1000
41 autocommit time in millisecond
42 committed if this time passes
43 received
44 fua (by default on
45 applicable only to persistent
46 when writing data from persist
47 underlying device
48 nofua
49 applicable only to persistent
50 flag when writing back data an
51 afterwards
52
53 - some underlying devices perf
54 with nofua. The user should
55 cleaner
56 when this option is activated
57 arguments or by a message), th
58 new writes (however, writes to
59 promoted, to avoid data corrup
60 writes) and it will gradually
61 data. The userspace can then m
62 process with "dmsetup status".
63 blocks drops to zero, userspac
64 dm-writecache target and repla
65 other targets.
66 max_age n
67 specifies the maximum age of a
68 a block is stored in the cache
69 written to the underlying devi
70 metadata_only
71 only metadata is promoted to t
72 improves performance for heavi
73 pause_writeback n (default: 3000
74 pause writeback if there was s
75 the origin volume in the last
76
77 Status:
78
79 1. error indicator - 0 if there was no error,
80 2. the number of blocks
81 3. the number of free blocks
82 4. the number of blocks under writeback
83 5. the number of read blocks
84 6. the number of read blocks that hit the cach
85 7. the number of write blocks
86 8. the number of write blocks that hit uncommi
87 9. the number of write blocks that hit committ
88 10. the number of write blocks that bypass the
89 11. the number of write blocks that are alloca
90 12. the number of write requests that are bloc
91 13. the number of flush requests
92 14. the number of discarded blocks
93
94 Messages:
95 flush
96 Flush the cache device. The me
97 if the cache device was flushe
98 flush_on_suspend
99 Flush the cache device on next
100 when you are going to remove t
101 sequence for removing the cach
102
103 1. send the "flush_on_suspend"
104 2. load an inactive table with
105 to the underlying device
106 3. suspend the device
107 4. ask for status and verify t
108 5. resume the device, so that
109 target
110 6. the cache device is now ina
111 cleaner
112 See above "cleaner" constructo
113 clear_stats
114 Clear the statistics that are
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