Bug 1163873

Summary: [RFE] LVM Thin: Add ability to set pool metadata area to read-only
Product: Red Hat Enterprise Linux 7 Reporter: Jonathan Earl Brassow <jbrassow>
Component: lvm2Assignee: Zdenek Kabelac <zkabelac>
lvm2 sub component: Thin Provisioning QA Contact: cluster-qe <cluster-qe>
Status: CLOSED DEFERRED Docs Contact:
Severity: unspecified    
Priority: unspecified CC: agk, cmarthal, heinzm, jbrassow, msnitzer, prajnoha, thornber, zkabelac
Version: 7.1Keywords: FutureFeature
Target Milestone: rc   
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: 1899206 (view as bug list) Environment:
Last Closed: 2020-11-18 18:01:30 UTC Type: Bug
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Bug Blocks: 1899206, 1119323    

Description Jonathan Earl Brassow 2014-11-13 15:47:39 UTC
Allow setting a pool to read-only-metadata mode.  This allows writes to the thins so long as they don't access unprovisioned areas.

Comment 3 Zdenek Kabelac 2015-06-19 19:47:05 UTC
Add for now lidbm function dm_tree_node_set_thin_pool_read_only()
with upstream patch.

https://www.redhat.com/archives/lvm-devel/2015-June/msg00054.html

Yet it's not quite clear what we should propose as lvm2 user API for this feature.

As the closest match with current lvm2 tools see we could see similarities with 'pvchange --allocateable y|n'.

So something like:  'lvchange --allocateable y|n  vg/pool' looks good - although the actual logic in thin-pool kernel target is slightly different, since kernel module avoid any modification of pool metadata - so it's not purely 'allocation related.

Other issue is - if user switch to 'read-only' mode - then ordinary filesystems do not handle well the case when some writes proceeds and some fail - but user should probably always use  'error-remount-ro' filesystem with thin volumes anyway.

Comment 7 Zdenek Kabelac 2020-11-18 18:01:30 UTC
For possible future enhancement cloned as upstream bug 1899206.