diff options
Diffstat (limited to 'Documentation/device-mapper/cache.txt')
-rw-r--r-- | Documentation/device-mapper/cache.txt | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt index e6b72d355151..68c0f517c60e 100644 --- a/Documentation/device-mapper/cache.txt +++ b/Documentation/device-mapper/cache.txt | |||
@@ -124,12 +124,11 @@ the default being 204800 sectors (or 100MB). | |||
124 | Updating on-disk metadata | 124 | Updating on-disk metadata |
125 | ------------------------- | 125 | ------------------------- |
126 | 126 | ||
127 | On-disk metadata is committed every time a REQ_SYNC or REQ_FUA bio is | 127 | On-disk metadata is committed every time a FLUSH or FUA bio is written. |
128 | written. If no such requests are made then commits will occur every | 128 | If no such requests are made then commits will occur every second. This |
129 | second. This means the cache behaves like a physical disk that has a | 129 | means the cache behaves like a physical disk that has a volatile write |
130 | write cache (the same is true of the thin-provisioning target). If | 130 | cache. If power is lost you may lose some recent writes. The metadata |
131 | power is lost you may lose some recent writes. The metadata should | 131 | should always be consistent in spite of any crash. |
132 | always be consistent in spite of any crash. | ||
133 | 132 | ||
134 | The 'dirty' state for a cache block changes far too frequently for us | 133 | The 'dirty' state for a cache block changes far too frequently for us |
135 | to keep updating it on the fly. So we treat it as a hint. In normal | 134 | to keep updating it on the fly. So we treat it as a hint. In normal |