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authorJens Axboe <axboe@kernel.dk>2013-07-02 08:32:57 +0200
committerJens Axboe <axboe@kernel.dk>2013-07-02 08:32:57 +0200
commitd0e3d0238d83b05d7846c7281524e0f814633dbd (patch)
tree9b3750123faf4975bde744bb9da9219fb697e374 /Documentation
parent5f0e5afa0de4522abb3ea7d1369039b94e740ec5 (diff)
parent8e51e414a3c6d92ef2cc41720c67342a8e2c0bf7 (diff)
downloadop-kernel-dev-d0e3d0238d83b05d7846c7281524e0f814633dbd.zip
op-kernel-dev-d0e3d0238d83b05d7846c7281524e0f814633dbd.tar.gz
Merge branch 'bcache-for-3.11' of git://evilpiepirate.org/~kent/linux-bcache into for-3.11/drivers
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/bcache.txt47
1 files changed, 29 insertions, 18 deletions
diff --git a/Documentation/bcache.txt b/Documentation/bcache.txt
index b3a7e7d..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
@@ -181,7 +185,7 @@ want for getting the best possible numbers when benchmarking.
In practice this isn't an issue because as soon as a write comes along it'll
cause the btree node to be split, and you need almost no write traffic for
- this to not show up enough to be noticable (especially since bcache's btree
+ this to not show up enough to be noticeable (especially since bcache's btree
nodes are huge and index large regions of the device). But when you're
benchmarking, if you're trying to warm the cache by reading a bunch of data
and there's no other traffic - that can be a problem.
@@ -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.
@@ -222,7 +229,7 @@ running
it's in passthrough mode or caching).
sequential_cutoff
- A sequential IO will bypass the cache once it passes this threshhold; the
+ A sequential IO will bypass the cache once it passes this threshold; the
most recent 128 IOs are tracked so sequential IO can be detected even when
it isn't all done at once.
@@ -296,10 +303,12 @@ cache_miss_collisions
since the synchronization for cache misses was rewritten)
cache_readaheads
- Count of times readahead occured.
+ Count of times readahead occurred.
SYSFS - CACHE SET:
+Available at /sys/fs/bcache/<cset-uuid>
+
average_key_size
Average data per key in the btree.
@@ -362,7 +371,7 @@ unregister
SYSFS - CACHE SET INTERNAL:
This directory also exposes timings for a number of internal operations, with
-separate files for average duration, average frequency, last occurence and max
+separate files for average duration, average frequency, last occurrence and max
duration: garbage collection, btree read, btree node sorts and btree splits.
active_journal_entries
@@ -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.
@@ -417,7 +428,7 @@ freelist_percent
space.
io_errors
- Number of errors that have occured, decayed by io_error_halflife.
+ Number of errors that have occurred, decayed by io_error_halflife.
metadata_written
Sum of all non data writes (btree writes and all other metadata).
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