linux.git/Documentation/device-mapper/cache.txt, branch v4.19

dm cache: Documentation: update default migration_throttling value

2018-01-30T21:55:47+00:00

In commit f8350daf7af0 ("dm cache: tune migration throttling") the
value for DEFAULT_MIGRATION_THRESHOLD was decreased from 204800 to
2048.  Edit device-mapper/cache.txt to reflect the correct default
value for migration_threshold.

Signed-off-by: John Pittman 
Signed-off-by: Mike Snitzer

dm cache: be consistent in specifying sectors and SI units in cache.txt

2018-01-17T14:16:09+00:00

Signed-off-by: mulhern 
Signed-off-by: Mike Snitzer

dm cache: delete obsoleted paragraph in cache.txt

2018-01-17T14:16:08+00:00

The 'mq' policy is no longer the default policy, and the default policy,
'smq', does not store hit counts.

Signed-off-by: mulhern 
Signed-off-by: Mike Snitzer

Documentation: device-mapper: cache.txt: Fix typos

2017-03-19T15:16:07+00:00

Fix a spelling error (hexidecimal->hexadecimal).

Signed-off-by: sayli karnik 
Signed-off-by: Jonathan Corbet

dm cache metadata: add "metadata2" feature

2017-02-16T18:12:47+00:00

If "metadata2" is provided as a table argument when creating/loading a
cache target a more compact metadata format, with separate dirty bits,
is used.  "metadata2" improves speed of shutting down a cache target.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm cache: display 'needs_check' in status if it is set

2015-07-16T14:23:50+00:00

There is currently no way to see that the needs_check flag has been set
in the metadata.  Display 'needs_check' in the cache status if it is set
in the cache metadata.

Also, update cache documentation.

Signed-off-by: Mike Snitzer

dm cache: add fail io mode and needs_check flag

2015-06-11T21:13:00+00:00

If a cache metadata operation fails (e.g. transaction commit) the
cache's metadata device will abort the current transaction, set a new
needs_check flag, and the cache will transition to "read-only" mode.  If
aborting the transaction or setting the needs_check flag fails the cache
will transition to "fail-io" mode.

Once needs_check is set the cache device will not be allowed to
activate.  Activation requires write access to metadata.  Future work is
needed to add proper support for running the cache in read-only mode.

Once in fail-io mode the cache will report a status of "Fail".

Also, add commit() wrapper that will disallow commits if in read_only or
fail mode.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer

dm thin: ensure user takes action to validate data and metadata consistency

2014-03-05T20:25:35+00:00

If a thin metadata operation fails the current transaction will abort,
whereby causing potential for IO layers up the stack (e.g. filesystems)
to have data loss.  As such, set THIN_METADATA_NEEDS_CHECK_FLAG in the
thin metadata's superblock which:
1) requires the user verify the thin metadata is consistent (e.g. use
   thin_check, etc)
2) suggests the user verify the thin data is consistent (e.g. use fsck)

The only way to clear the superblock's THIN_METADATA_NEEDS_CHECK_FLAG is
to run thin_repair.

On metadata operation failure: abort current metadata transaction, set
pool in read-only mode, and now set the needs_check flag.

As part of this change, constraints are introduced or relaxed:
* don't allow a pool to transition to write mode if needs_check is set
* don't allow data or metadata space to be resized if needs_check is set
* if a thin pool's metadata space is exhausted: the kernel will now
  force the user to take the pool offline for repair before the kernel
  will allow the metadata space to be extended.

Also, update Documentation to include information about when the thin
provisioning target commits metadata, how it handles metadata failures
and running out of space.

Signed-off-by: Mike Snitzer 
Signed-off-by: Joe Thornber

dm cache: add policy name to status output

2014-01-16T18:44:11+00:00

The cache's policy may have been established using the "default" alias,
which is currently the "mq" policy but the default policy may change in
the future.  It is useful to know exactly which policy is being used.

Add a 'real' member to the dm_cache_policy_type structure and have the
"default" dm_cache_policy_type point to the real "mq"
dm_cache_policy_type.  Update dm_cache_policy_get_name() to check if
real is set, if so report the name of the real policy (not the alias).

Requested-by: Jonathan Brassow 
Signed-off-by: Mike Snitzer

dm cache: add block sizes and total cache blocks to status output

2014-01-10T15:24:33+00:00

Improve cache_status to emit:
 <#used metadata blocks>/<#total metadata blocks>
 <#used cache blocks>/<#total cache blocks>
...

Adding the block sizes allows for easier calculation of the overall size
of both the metadata and cache devices.  Adding <#total cache blocks>
provides useful context for how much of the cache is used.

Unfortunately these additions to the status will require updates to
users' scripts that monitor the cache status.  But these changes help
provide more comprehensive information about the cache device and will
simplify tools that are being developed to manage dm-cache devices --
because they won't need to issue 3 operations to cobble together the
information that we can easily provide via a single status ioctl.

While updating the status documentation in cache.txt spaces were
tabify'd.

Requested-by: Jonathan Brassow 
Signed-off-by: Mike Snitzer 
Acked-by: Joe Thornber