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Diffstat (limited to 'Documentation/bcache.txt')
| -rw-r--r-- | Documentation/bcache.txt | 49 |
1 files changed, 33 insertions, 16 deletions
diff --git a/Documentation/bcache.txt b/Documentation/bcache.txt index 2cdd4cfc6912..32b6c3189d98 100644 --- a/Documentation/bcache.txt +++ b/Documentation/bcache.txt @@ -46,29 +46,33 @@ you format your backing devices and cache device at the same time, you won't have to manually attach: make-bcache -B /dev/sda /dev/sdb -C /dev/sdc -To make bcache devices known to the kernel, echo them to /sys/fs/bcache/register: +bcache-tools now ships udev rules, and bcache devices are known to the kernel +immediately. Without udev, you can manually register devices like this: echo /dev/sdb > /sys/fs/bcache/register echo /dev/sdc > /sys/fs/bcache/register -To register your bcache devices automatically, you could add something like -this to an init script: +Registering the backing device makes the bcache device show up in /dev; you can +now format it and use it as normal. But the first time using a new bcache +device, it'll be running in passthrough mode until you attach it to a cache. +See the section on attaching. - echo /dev/sd* > /sys/fs/bcache/register_quiet +The devices show up as: -It'll look for bcache superblocks and ignore everything that doesn't have one. + /dev/bcache<N> -Registering the backing device makes the bcache show up in /dev; you can now -format it and use it as normal. But the first time using a new bcache device, -it'll be running in passthrough mode until you attach it to a cache. See the -section on attaching. +As well as (with udev): -The devices show up at /dev/bcacheN, and can be controlled via sysfs from -/sys/block/bcacheN/bcache: + /dev/bcache/by-uuid/<uuid> + /dev/bcache/by-label/<label> + +To get started: mkfs.ext4 /dev/bcache0 mount /dev/bcache0 /mnt +You can control bcache devices through sysfs at /sys/block/bcache<N>/bcache . + Cache devices are managed as sets; multiple caches per set isn't supported yet but will allow for mirroring of metadata and dirty data in the future. Your new cache set shows up as /sys/fs/bcache/<UUID> @@ -80,11 +84,11 @@ must be attached to your cache set to enable caching. Attaching a backing device to a cache set is done thusly, with the UUID of the cache set in /sys/fs/bcache: - echo <UUID> > /sys/block/bcache0/bcache/attach + echo <CSET-UUID> > /sys/block/bcache0/bcache/attach This only has to be done once. The next time you reboot, just reregister all your bcache devices. If a backing device has data in a cache somewhere, the -/dev/bcache# device won't be created until the cache shows up - particularly +/dev/bcache<N> device won't be created until the cache shows up - particularly important if you have writeback caching turned on. If you're booting up and your cache device is gone and never coming back, you @@ -191,6 +195,9 @@ want for getting the best possible numbers when benchmarking. SYSFS - BACKING DEVICE: +Available at /sys/block/<bdev>/bcache, /sys/block/bcache*/bcache and +(if attached) /sys/fs/bcache/<cset-uuid>/bdev* + attach Echo the UUID of a cache set to this file to enable caching. @@ -300,6 +307,8 @@ cache_readaheads SYSFS - CACHE SET: +Available at /sys/fs/bcache/<cset-uuid> + average_key_size Average data per key in the btree. @@ -319,7 +328,10 @@ cache<0..n> Symlink to each of the cache devices comprising this cache set. cache_available_percent - Percentage of cache device free. + Percentage of cache device which doesn't contain dirty data, and could + potentially be used for writeback. This doesn't mean this space isn't used + for clean cached data; the unused statistic (in priority_stats) is typically + much lower. clear_stats Clears the statistics associated with this cache @@ -387,6 +399,8 @@ trigger_gc SYSFS - CACHE DEVICE: +Available at /sys/block/<cdev>/bcache + block_size Minimum granularity of writes - should match hardware sector size. @@ -423,8 +437,11 @@ nbuckets Total buckets in this cache priority_stats - Statistics about how recently data in the cache has been accessed. This can - reveal your working set size. + Statistics about how recently data in the cache has been accessed. + This can reveal your working set size. Unused is the percentage of + the cache that doesn't contain any data. Metadata is bcache's + metadata overhead. Average is the average priority of cache buckets. + Next is a list of quantiles with the priority threshold of each. written Sum of all data that has been written to the cache; comparison with |