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dm thin: add read only and fail io modes

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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>
This commit is contained in:
Joe Thornber
2012-07-27 15:08:16 +01:00
committed by Alasdair G Kergon
parent da105ed5fd
commit e49e582965
2 changed files with 347 additions and 99 deletions
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24
Documentation/device-mapper/thin-provisioning.txt
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@@ -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.