diff options
Diffstat (limited to 'Documentation/bcache.txt')
| -rw-r--r-- | Documentation/bcache.txt | 37 |
1 files changed, 24 insertions, 13 deletions
diff --git a/Documentation/bcache.txt b/Documentation/bcache.txt index c3365f2..32b6c31 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. @@ -390,6 +399,8 @@ trigger_gc SYSFS - CACHE DEVICE: +Available at /sys/block/<cdev>/bcache + block_size Minimum granularity of writes - should match hardware sector size. |
