linux-toradex.git/Documentation/device-mapper/thin-provisioning.txt, branch v4.10

dm thin: 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 thin-pool status if it is
set in the thinp metadata.

Also, update thinp documentation.

Signed-off-by: Mike Snitzer

dm thin: remove stale 'trim' message documentation

2015-04-15T16:10:22+00:00

The 'trim' message wasn't ever implemented.

Signed-off-by: Mike Snitzer

dm thin: add 'no_space_timeout' dm-thin-pool module param

2014-05-20T18:30:36+00:00

Commit 85ad643b ("dm thin: add timeout to stop out-of-data-space mode
holding IO forever") introduced a fixed 60 second timeout.  Users may
want to either disable or modify this timeout.

Allow the out-of-data-space timeout to be configured using the
'no_space_timeout' dm-thin-pool module param.  Setting it to 0 will
disable the timeout, resulting in IO being queued until more data space
is added to the thin-pool.

Signed-off-by: Mike Snitzer 
Cc: stable@vger.kernel.org # 3.14+

dm thin: fix Documentation for held metadata root feature

2014-03-06T19:23:35+00:00

The Documentation for the thin provisioning target's held metadata root
feature was incorrect.  It is now available and the value for the held
metadata root is in block units (not 512b sectors).

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 thin: add error_if_no_space feature

2014-01-07T15:14:30+00:00

If the pool runs out of data or metadata space, the pool can either
queue or error the IO destined to the data device.  The default is to
queue the IO until more space is added.

An admin may now configure the pool to error IO when no space is
available by setting the 'error_if_no_space' feature when loading the
thin-pool table.

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

dm thin: add data block size limits to Documentation

2013-08-23T13:02:14+00:00

Inform users that the data block size can't be any arbitrary number,
i.e. its value must be between 64KB and 1GB.  Also, it should be a
multiple of 64KB.

Signed-off-by: Carlos Maiolino 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon 
Acked-by: Joe Thornber

dm thin: add read only and fail io modes

2012-07-27T14:08:16+00:00

Add read-only and fail-io modes to thin provisioning.

If a transaction commit fails the pool's metadata device will transition
to "read-only" mode.  If a commit fails once already in read-only mode
the transition to "fail-io" mode occurs.

Once in fail-io mode the pool and all associated thin devices will
report a status of "Fail".

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon

dm thin: provide userspace access to pool metadata

2012-06-02T23:30:01+00:00

This patch implements two new messages that can be sent to the thin
pool target allowing it to take a snapshot of the _metadata_.  This,
read-only snapshot can be accessed by userland, concurrently with the
live target.

Only one metadata snapshot can be held at a time.  The pool's status
line will give the block location for the current msnap.

Since version 0.1.5 of the userland thin provisioning tools, the
thin_dump program displays the msnap as follows:

    thin_dump -m  

Available here: https://github.com/jthornber/thin-provisioning-tools

Now that userland can access the metadata we can do various things
that have traditionally been kernel side tasks:

     i) Incremental backups.

     By using metadata snapshots we can work out what blocks have
     changed over time.  Combined with data snapshots we can ensure
     the data doesn't change while we back it up.

     A short proof of concept script can be found here:

     https://github.com/jthornber/thinp-test-suite/blob/master/incremental_backup_example.rb

     ii) Migration of thin devices from one pool to another.

     iii) Merging snapshots back into an external origin.

     iv) Asyncronous replication.

Signed-off-by: Joe Thornber 
Signed-off-by: Alasdair G Kergon

dm thin: add pool target flags to control discard

2012-03-28T17:41:29+00:00

Add dm thin target arguments to control discard support.

ignore_discard: Disables discard support

no_discard_passdown: Don't pass discards down to the underlying data
device, but just remove the mapping within the thin provisioning target.

Signed-off-by: Joe Thornber 
Signed-off-by: Mike Snitzer 
Signed-off-by: Alasdair G Kergon