[LU-10192] Agent entry for cross-MDTs reference

Related — Fri, 31 Aug 2018 08:11:54 +0000

In DNE environment, the object and its name entry may reside on different MDTs. Under such case, we will create an agent entry under backend REMOTE_PARENT_DIR directory on the MDT where the object resides. The agent entry references the object locally. If without the agent entry, related object will be invisible for MDT side file level backup restore by userspace tool, such as 'tar'.

ldiskfs supports agent entry. After migrated to ZFS, the agent entry will be on ZFS backend. ZFS needs to handle it to avoid dangling.

On the other hand, there may be a lot of corss-MDTs reference for regular file. That may make the single REMOTE_PARENT_DIR very fat as to quite slow for being operated. So it is preferred to optimised that with multiple REMOTE_PARENT_DIRs, may be per MDT per REMOTE_PARENT_DIR.

Whamcloud Community JIRA

[LU-10192] Agent entry for cross-MDTs reference