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 <snitzer@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
It was always intended that a user could provide a thin metadata device
that is larger than the max supported by the on-disk format. The extra
space would just go unused.
Unfortunately that never worked. If the user attempted to use a larger
metadata device on creation they would get an error like the following:
device-mapper: space map common: space map too large
device-mapper: transaction manager: couldn't create metadata space map
device-mapper: thin metadata: tm_create_with_sm failed
device-mapper: table: 252:17: thin-pool: Error creating metadata object
device-mapper: ioctl: error adding target to table
Fix this by allowing the initial metadata space map creation to cap its
size at the max number of blocks supported (DM_SM_METADATA_MAX_BLOCKS).
get_metadata_dev_size() must also impose DM_SM_METADATA_MAX_BLOCKS (via
THIN_METADATA_MAX_SECTORS), otherwise extending metadata would cap at
THIN_METADATA_MAX_SECTORS_WARNING (which is larger than supported).
Also, the calculation for THIN_METADATA_MAX_SECTORS didn't account for
the sizeof the disk_bitmap_header. So the supported maximum metadata
size is a bit smaller (reduced from 33423360 to 33292800 sectors).
Lastly, remove the "excess space will not be used" warning message from
get_metadata_dev_size(); it resulted in printing the warning multiple
times. Factor out warn_if_metadata_device_too_big(), call it from
pool_ctr() and maybe_resize_metadata_dev().
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Commit 905e51b ("dm thin: commit outstanding data every second")
introduced a periodic commit. This commit occurs regardless of whether
any thin devices have made changes.
Fix the periodic commit to check if any of a pool's thin devices have
changed using dm_pool_changed_this_transaction().
Reported-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org
Also, move 'err' member in dm_thin_new_mapping structure to eliminate 4
byte hole (reduces size from 88 bytes to 80).
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
If a snapshot is created and later deleted the origin dm_thin_device's
snapshotted_time will have been updated to reflect the snapshot's
creation time. The 'shared' flag in the dm_thin_lookup_result struct
returned from dm_thin_find_block() is an approximation based on
snapshotted_time -- this is done to avoid 0(n), or worse, time
complexity. In this case, the shared flag would be true.
But because the 'shared' flag reflects an approximation a block can be
incorrectly assumed to be shared (e.g. false positive for 'shared'
because the snapshot no longer exists). This could result in discards
issued to a thin device not being passed down to the pool's underlying
data device.
To fix this we double check that a thin block is really still in-use
after a mapping is removed using dm_pool_block_is_used(). If the
reference count for a block is now zero the discard is allowed to be
passed down.
Also add a 'definitely_not_shared' member to the dm_thin_new_mapping
structure -- reflects that the 'shared' flag in the response from
dm_thin_find_block() can only be held as definitive if false is
returned.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1043527
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
A thin-pool may be in read-only mode because the pool's data or metadata
space was exhausted. To allow for recovery, by adding more space to the
pool, we must allow a pool to transition from PM_READ_ONLY to PM_WRITE
mode. Otherwise, running out of space will render the pool permanently
read-only.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Generate a dm event when the amount of remaining thin pool metadata
space falls below a certain level.
The threshold is taken to be a quarter of the size of the metadata
device with a minimum threshold of 4MB.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Allow the dm thin pool metadata device to be extended.
Whenever a pool is resumed, detect whether the size of the metadata
device has increased, and if so, extend the metadata to use the new
space.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Introduce dm_pool_abort_metadata to abort the current metadata
transaction. Generally this will only be called when bad things are
happening and dm-thin is trying to roll back to a good state for
read-only mode.
It's complicated by the fact that the metadata device may have failed
completely causing the abort to be unable to read the old transaction.
In this case the metadata object is placed in a 'fail' mode and
everything fails apart from destroying it.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Introduce dm_pool_metadata_set_read_only to put the underlying block
manager into read-only mode.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Introduce dm_thin_changed_this_transaction to dm-thin-metadata to publish a
useful bit of information we're already tracking. This will help dm thin
decide when to commit.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Add a parameter to dm_pool_metadata_open to indicate whether or not an
unformatted metadata area should be formatted.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Clean up "warning: dubious: !x & y". Also make it clear that
__snapshotted_since() returns a bool and that dm_thin_lookup_result's
'shared' member is a flag.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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 <msnap root> <metadata dev>
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 <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
The thin metadata format can only make use of a device that is <=
THIN_METADATA_MAX_SECTORS (currently 15.9375 GB). Therefore, there is no
practical benefit to using a larger device.
However, it may be that other factors impose a certain granularity for
the space that is allocated to a device (E.g. lvm2 can impose a coarse
granularity through the use of large, >= 1 GB, physical extents).
Rather than reject a larger metadata device, during thin-pool device
construction, switch to allowing it but issue a warning if a device
larger than THIN_METADATA_MAX_SECTORS_WARNING (16 GB) is
provided. Any space over 15.9375 GB will not be used.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Initial EXPERIMENTAL implementation of device-mapper thin provisioning
with snapshot support. The 'thin' target is used to create instances of
the virtual devices that are hosted in the 'thin-pool' target. The
thin-pool target provides data sharing among devices. This sharing is
made possible using the persistent-data library in the previous patch.
The main highlight of this implementation, compared to the previous
implementation of snapshots, is that it allows many virtual devices to
be stored on the same data volume, simplifying administration and
allowing sharing of data between volumes (thus reducing disk usage).
Another big feature is support for arbitrary depth of recursive
snapshots (snapshots of snapshots of snapshots ...). The previous
implementation of snapshots did this by chaining together lookup tables,
and so performance was O(depth). This new implementation uses a single
data structure so we don't get this degradation with depth.
For further information and examples of how to use this, please read
Documentation/device-mapper/thin-provisioning.txt
Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
