dm thin: add read only and fail io modes
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>
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index f5cfc62..30b8b83 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -231,6 +231,9 @@
no_discard_passdown: Don't pass discards down to the underlying
data device, but just remove the mapping.
+ read_only: Don't allow any changes to be made to the pool
+ metadata.
+
Data block size must be between 64KB (128 sectors) and 1GB
(2097152 sectors) inclusive.
@@ -239,7 +242,7 @@
<transaction id> <used metadata blocks>/<total metadata blocks>
<used data blocks>/<total data blocks> <held metadata root>
-
+ [no_]discard_passdown ro|rw
transaction id:
A 64-bit number used by userspace to help synchronise with metadata
@@ -257,6 +260,21 @@
held root. This feature is not yet implemented so '-' is
always returned.
+ discard_passdown|no_discard_passdown
+ Whether or not discards are actually being passed down to the
+ underlying device. When this is enabled when loading the table,
+ it can get disabled if the underlying device doesn't support it.
+
+ ro|rw
+ If the pool encounters certain types of device failures it will
+ drop into a read-only metadata mode in which no changes to
+ the pool metadata (like allocating new blocks) are permitted.
+
+ In serious cases where even a read-only mode is deemed unsafe
+ no further I/O will be permitted and the status will just
+ contain the string 'Fail'. The userspace recovery tools
+ should then be used.
+
iii) Messages
create_thin <dev id>
@@ -329,3 +347,7 @@
ii) Status
<nr mapped sectors> <highest mapped sector>
+
+ If the pool has encountered device errors and failed, the status
+ will just contain the string 'Fail'. The userspace recovery
+ tools should then be used.
