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  • Latest Post - ‏2014-12-09T19:08:09Z by pkulkarn
7 Posts

Pinned topic After a cache outage, how to determine --failover-time to pull files from home to cache?

‏2014-05-21T18:33:05Z | afm cache home

In the GPFS Advanced Admin Guide AFM chapter, it says to pull files from home to cache using the following command:

# mmafmctl FileSystem failback -j Fileset --start --failover-time 'TimeIncludingTimezone'

How do you determine the correct failover time in order to get all new home content?

  • pkulkarn
    12 Posts

    Re: After a cache outage, how to determine --failover-time to pull files from home to cache?


    Caches can be down either permanently due to disaster or temporarily due to maintenance.Applications can be moved to the home cluster. The nature of AFM is to push the data asynchronously, so the cache might have pending updates that have not been pushed to home at the time when the applications are moved. In cases where application semantics allow them to move from cache to home with pending updates still in cache, it is possible that files at home will change along with the pending data in cache. 

    Once the cache comes back, the first access will drive the cache to push stale data to home. This might result in a stale pending update to overwrite the latest data written at home while the cache was down. In these cases, failback procedure needs to followed so that latest data is preserved and old or stale data is discarded. The data staleness is determined based on file mtime and failover time.

    Failover time is when the applications were moved to home for home access [in case of cache outage] or the time when the failover command is executed in case of  maintenance.