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bcache: Refresh usage docs

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

Signed-off-by: Gabriel de Perthuis <g2p.code@gmail.com>
Signed-off-by: Kent Overstreet <koverstreet@google.com>
This commit is contained in:
Gabriel de Perthuis 2013-06-27 02:12:07 +02:00 committed by Kent Overstreet
parent ab9e14002e
commit cecd628d9a
1 changed files with 24 additions and 13 deletions
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Documentation/bcache.txt
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@ -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.