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[firefly-linux-kernel-4.4.55.git] / Documentation / bcache.txt

diff --git a/Documentation/bcache.txt b/Documentation/bcache.txt
index b3a7e7d384f6583ede08ffec4957c6f40c45172b..32b6c3189d9826a53875ae6dc51ce62e9b86778b 100644 (file)
--- 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).