diff options
Diffstat (limited to 'Documentation/device-mapper/cache.txt')
| -rw-r--r-- | Documentation/device-mapper/cache.txt | 62 |
1 files changed, 34 insertions, 28 deletions
diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt index 719320b5ed3f..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). Updating on-disk metadata ------------------------- -On-disk metadata is committed every time a REQ_SYNC or REQ_FUA bio is -written. If no such requests are made then commits will occur every -second. This means the cache behaves like a physical disk that has a -write cache (the same is true of the thin-provisioning target). If -power is lost you may lose some recent writes. The metadata should -always be consistent in spite of any crash. +On-disk metadata is committed every time a FLUSH or FUA bio is written. +If no such requests are made then commits will occur every second. This +means the cache behaves like a physical disk that has a volatile write +cache. If power is lost you may lose some recent writes. The metadata +should always be consistent in spite of any crash. The 'dirty' state for a cache block changes far too frequently for us to keep updating it on the fly. So we treat it as a hint. In normal @@ -217,36 +216,43 @@ the characteristics of a specific policy, always request it by name. Status ------ -<#used metadata blocks>/<#total metadata blocks> <#read hits> <#read misses> -<#write hits> <#write misses> <#demotions> <#promotions> <#blocks in cache> -<#dirty> <#features> <features>* <#core args> <core args>* <#policy args> -<policy args>* - -#used metadata blocks : Number of metadata blocks used -#total metadata blocks : Total number of metadata blocks -#read hits : Number of times a READ bio has been mapped +<metadata block size> <#used metadata blocks>/<#total metadata blocks> +<cache block size> <#used cache blocks>/<#total cache blocks> +<#read hits> <#read misses> <#write hits> <#write misses> +<#demotions> <#promotions> <#dirty> <#features> <features>* +<#core args> <core args>* <policy name> <#policy args> <policy args>* + +metadata block size : Fixed block size for each metadata block in + sectors +#used metadata blocks : Number of metadata blocks used +#total metadata blocks : Total number of metadata blocks +cache block size : Configurable block size for the cache device + in sectors +#used cache blocks : Number of blocks resident in the cache +#total cache blocks : Total number of cache blocks +#read hits : Number of times a READ bio has been mapped to the cache -#read misses : Number of times a READ bio has been mapped +#read misses : Number of times a READ bio has been mapped to the origin -#write hits : Number of times a WRITE bio has been mapped +#write hits : Number of times a WRITE bio has been mapped to the cache -#write misses : Number of times a WRITE bio has been +#write misses : Number of times a WRITE bio has been mapped to the origin -#demotions : Number of times a block has been removed +#demotions : Number of times a block has been removed from the cache -#promotions : Number of times a block has been moved to +#promotions : Number of times a block has been moved to the cache -#blocks in cache : Number of blocks resident in the cache -#dirty : Number of blocks in the cache that differ +#dirty : Number of blocks in the cache that differ from the origin -#feature args : Number of feature args to follow -feature args : 'writethrough' (optional) -#core args : Number of core arguments (must be even) -core args : Key/value pairs for tuning the core +#feature args : Number of feature args to follow +feature args : 'writethrough' (optional) +#core args : Number of core arguments (must be even) +core args : Key/value pairs for tuning the core e.g. migration_threshold -#policy args : Number of policy arguments to follow (must be even) -policy args : Key/value pairs - e.g. 'sequential_threshold 1024 +policy name : Name of the policy +#policy args : Number of policy arguments to follow (must be even) +policy args : Key/value pairs + e.g. sequential_threshold Messages -------- |