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path: root/Documentation/device-mapper/thin-provisioning.txt
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2015-07-16dm thin: display 'needs_check' in status if it is setMike Snitzer
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 <snitzer@redhat.com>
2015-04-15dm thin: remove stale 'trim' message documentationMike Snitzer
The 'trim' message wasn't ever implemented. Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2014-05-20dm thin: add 'no_space_timeout' dm-thin-pool module paramMike Snitzer
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 <snitzer@redhat.com> Cc: stable@vger.kernel.org # 3.14+
2014-03-06dm thin: fix Documentation for held metadata root featureMike Snitzer
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 <snitzer@redhat.com>
2014-03-05dm thin: ensure user takes action to validate data and metadata consistencyMike Snitzer
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>
2014-01-07dm thin: add error_if_no_space featureMike Snitzer
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 <snitzer@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com>
2013-08-23dm thin: add data block size limits to DocumentationCarlos Maiolino
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 <cmaiolino@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com>
2012-07-27dm thin: add read only and fail io modesJoe Thornber
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 <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2012-06-02dm thin: provide userspace access to pool metadataJoe Thornber
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>
2012-03-28dm thin: add pool target flags to control discardJoe Thornber
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 <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2012-03-28dm thin: support read only external snapshot originsJoe Thornber
Support the use of an external _read only_ device as an origin for a thin device. Any read to an unprovisioned area of the thin device will be passed through to the origin. Writes trigger allocation of new blocks as usual. One possible use case for this would be VM hosts that want to run guests on thinly-provisioned volumes but have the base image on another device (possibly shared between many VMs). 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>
2012-03-28dm thin: relax hard limit on the maximum size of a metadata deviceMike Snitzer
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>
2012-03-28dm thin: correct commentsJoe Thornber
Remove documentation for unimplemented 'trim' message. I'd planned a 'trim' target message for shrinking thin devices, but this is better handled via the discard ioctl. 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>
2012-02-21Documentation: Fix typo in thin-provisioning.txtMasanari Iida
Correct spelling "descibes" to "describes" in Documentation/device-mapper/thin-provisioning.txt Signed-off-by: Masanari Iida <standby24x7@gmail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-10-31dm: add thin provisioning targetJoe Thornber
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>