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OCFS2/DesignDocs/ReadOnly

OCFS2 readonly support

Mark Fasheh <mark dot fasheh at oracle dot com>

August 31, 2005

Goals / Requirements

Support two levels of readonly-ness. To a user on the system, all of these will disallow modifications to files and their metadata. They differ only in restrictions "under the hood"

Give OCFS2 the ability to go to / from a given readonly mode for a given number of conditions:

Restrictions

We only support one mount option 'ro'. The file system will do a soft readonly mount unless it detects a readonly device, in which case it prints a useful message (much like ext3) and goes hard readonly.

User will not be allowed to remount when in hard readonly mode - it is extremely difficult to resolve the state differences between the cluster and a node which has been reading old or invalid data.

Generally, system errors will send the file system into soft readonly. Hard readonly is reserved for bad disk problems (journal failures, etc) or cluster events such as loss of network, heartbeat self fencing, etc.


2012-11-08 13:01