28 September 2009

Replicating like HOT cakes

As mentioned on the storage list, the newest versions of the GridPP DPM Tools (documented at http://www.gridpp.ac.uk/wiki/DPM-admin-tools) contain a tool to replicate files within a spacetoken (such as the ATLASHOTDISK).

At Edinburgh this is running in cron

0 1 * * * root /opt/lcg/bin/dpm-sql-spacetoken-replicate-hotfiles --st ATLASHOTDISK >> /var/log/dpmrephotfiles.log 2>&1

Some issues observed are :
* Takes quite a long time to run the first time. Because of all the dpm-replicate calls on the ~1000 files that ATLAS stuck in there it took around 4 hours just for 1 extra copy. Since then though only the odd file has come in - so it doesn't have much to do.
* The replicas are always on different filesystems - but not always different disk server. This obviously depends on how many servers you have for that pool (compared to the nreps you want), as well as how many filesystems on each server. The replica creation could be more directed but perhaps it should be the default behaviour of the built in command to use a different server if it can.

Intended future enhancements of this tool include:
* List in a clear way the physical duplicates in the ST.
* Remove excess duplicates.
* Automatic replications of a list of "hotfiles"

Other suggestions welcome.

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