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Commit cecd628d authored by Gabriel de Perthuis's avatar Gabriel de Perthuis Committed by Kent Overstreet
Browse files

bcache: Refresh usage docs 



Mention udev autoregistration, symlinks.  Write down some sysfs paths.

Signed-off-by: default avatarGabriel de Perthuis <g2p.code@gmail.com>
Signed-off-by: default avatarKent Overstreet <koverstreet@google.com>
parent ab9e1400

Documentation/bcache.txt

+24 −13
Original line number Original line Diff line number Diff line
@@ -46,29 +46,33 @@ you format your backing devices and cache device at the same time, you won't 
have to manually attach:

have to manually attach:

  make-bcache -B /dev/sda /dev/sdb -C /dev/sdc

  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/sdb > /sys/fs/bcache/register

  echo /dev/sdc > /sys/fs/bcache/register

  echo /dev/sdc > /sys/fs/bcache/register





To register your bcache devices automatically, you could add something like

Registering the backing device makes the bcache device show up in /dev; you can

this to an init script:

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

As well as (with udev):

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.





The devices show up at /dev/bcacheN, and can be controlled via sysfs from

  /dev/bcache/by-uuid/<uuid>

/sys/block/bcacheN/bcache:

  /dev/bcache/by-label/<label>



To get started:





  mkfs.ext4 /dev/bcache0

  mkfs.ext4 /dev/bcache0

  mount /dev/bcache0 /mnt

  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

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

but will allow for mirroring of metadata and dirty data in the future. Your new

cache set shows up as /sys/fs/bcache/<UUID>

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

device to a cache set is done thusly, with the UUID of the cache set in

/sys/fs/bcache:

/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

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

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.

important if you have writeback caching turned on.





If you're booting up and your cache device is gone and never coming back, you

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:

SYSFS - BACKING DEVICE:





Available at /sys/block/<bdev>/bcache, /sys/block/bcache*/bcache and

(if attached) /sys/fs/bcache/<cset-uuid>/bdev*



attach

attach

  Echo the UUID of a cache set to this file to enable caching.

  Echo the UUID of a cache set to this file to enable caching.
@@ -300,6 +307,8 @@ cache_readaheads 




SYSFS - CACHE SET:

SYSFS - CACHE SET:





Available at /sys/fs/bcache/<cset-uuid>



average_key_size

average_key_size

  Average data per key in the btree.

  Average data per key in the btree.
@@ -390,6 +399,8 @@ trigger_gc 




SYSFS - CACHE DEVICE:

SYSFS - CACHE DEVICE:





Available at /sys/block/<cdev>/bcache



block_size

block_size

  Minimum granularity of writes - should match hardware sector size.

  Minimum granularity of writes - should match hardware sector size.