Lines Matching refs:a
8 dm-cache is a device mapper target written by Joe Thornber, Heinz
11 It aims to improve performance of a block device (eg, a spindle) by
12 dynamically migrating some of its data to a faster, smaller device
17 a thin-provisioning pool. Caching solutions that are integrated more
23 The decision as to what data to migrate and when is left to a plug-in
26 scenarios (eg. a vm image server).
32 Movement of the primary copy of a logical block from one
39 The origin device always contains a copy of the logical block, which
60 e.g. as a mirror for extra robustness. This metadata device may only
61 be used by a single cache device.
66 The origin is divided up into blocks of a fixed size. This block size
69 sectors (32KB) and 2097152 sectors (1GB) and a multiple of 64 sectors (32KB).
71 Having a fixed block size simplifies the target a lot. But it is
72 something of a compromise. For instance, a small part of a block may be
73 getting hit a lot, yet the whole block will be promoted to the cache.
84 If writeback, the default, is selected then a write to a block that is
88 If writethrough is selected then a write to a cached block will not
97 Passthrough mode allows a cache device to be activated without having to
107 dirty blocks in a cache. Useful for decommissioning a cache or when
108 shrinking a cache. Shrinking the cache's fast device requires all cache
114 modes already maintain a clean cache. Future support to partially clean
115 the cache, above a specified threshold, will allow for keeping the cache
122 The user can set a throttle to prevent more than a certain amount of
127 For the time being, a message "migration_threshold <#sectors>"
134 On-disk metadata is committed every time a FLUSH or FUA bio is written.
136 means the cache behaves like a physical disk that has a volatile write
140 The 'dirty' state for a cache block changes far too frequently for us
141 to keep updating it on the fly. So we treat it as a hint. In normal
148 Policy plug-ins can store a chunk of data per cache block. It's up to
150 dirty flags this data is lost if there's a crash so a safe fallback
159 need a generic way of getting and setting these. Device-mapper
167 whole block device. We store a bitset tracking the discard state of
168 blocks. However, we allow this bitset to have a different block size
212 passthrough a degraded mode useful for various cache coherency
215 the origin. If a write goes to a cached origin
220 bits in a separate btree, which improves speed of
231 the characteristics of a specific policy, always request it by name.
255 #read hits Number of times a READ bio has been mapped
257 #read misses Number of times a READ bio has been mapped
259 #write hits Number of times a WRITE bio has been mapped
261 #write misses Number of times a WRITE bio has been
263 #demotions Number of times a block has been removed
265 #promotions Number of times a block has been moved to
279 In serious cases where even a read-only mode is
296 need a generic way of getting and setting these. Device-mapper
311 range's end value is "one past the end", meaning 5-10 expresses a range
312 of values from 5 to 9. Each cblock must be expressed as a decimal
313 value, in the future a variant message that takes cblock ranges