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authorJoe Thornber <ejt@redhat.com>2012-07-27 15:08:16 +0100
committerAlasdair G Kergon <agk@redhat.com>2012-07-27 15:08:16 +0100
commite49e582965b3694f07a106adc83ddb44aa4f0890 (patch)
treefcc6ff02fd4bd9afa59b5fd3bdbb9991f1271d8a /Documentation
parentda105ed5fd7edcc5e0df7dbacef4dadda74e7ebe (diff)
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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/device-mapper/thin-provisioning.txt24
1 files changed, 23 insertions, 1 deletions
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index f5cfc62b7ad3..30b8b83bd333 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -231,6 +231,9 @@ i) Constructor
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 @@ ii) Status
<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 @@ ii) Status
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 @@ regain some space then send the 'trim' message to the pool.
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.