path: root/Documentation
diff options
authorJoe Thornber <ejt@redhat.com>2012-06-03 00:30:01 +0100
committerAlasdair G Kergon <agk@redhat.com>2012-06-03 00:30:01 +0100
commitcc8394d86f045b86ff303d3c9e4ce47d97148951 (patch)
treead37143c9709f523fb2ca9fc5ac9de75e9a011f9 /Documentation
parentdm thin: use slab mempools (diff)
dm thin: provide userspace access to pool metadata
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>
Diffstat (limited to 'Documentation')
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 3370bc4d7b98..f5cfc62b7ad3 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -287,6 +287,17 @@ iii) Messages
the current transaction id is when you change it with this
compare-and-swap message.
+ reserve_metadata_snap
+ Reserve a copy of the data mapping btree for use by userland.
+ This allows userland to inspect the mappings as they were when
+ this message was executed. Use the pool's status command to
+ get the root block associated with the metadata snapshot.
+ release_metadata_snap
+ Release a previously reserved copy of the data mapping btree.
'thin' target