On Tue, Nov 19, 2019 at 6:45 PM karthick rn <karthick.narend...@gmail.com> wrote: > > Hi, > > When provisioning multiple volumes, for ex. HDFS & Azure Data Lake storage, > it would be good to choose which volume we want the system tables like > metadata, root, replication tables to be created. Currently, Accumulo > randomly creates these tables on multiple volumes and the only way to > control this is to run Accumulo init on 1st volume so all system tables get > created on this volume and then add the other volumes. > > I have also tried running 'config -t accumulo.metadata -s > table.custom.volume.preferred=hdfs://accucluster/accumulo' in an attempt to > move the metadata table to a preferred volume, in this case HDFS, but I > don’t see metadata table under HDFS. Also, ‘config -f > table.custom.volume.preferred’ does not show anything! > In short, I was wondering if there is any provision to "move" these system > tables across volumes, or is that a non-goal by design?
Accumulo volume choices are currently sticky. Each tablet chooses a volume where it will put files and it remembers that choice (stored in the metadata table under the srv:dir column). After that choice is made, the tablet will always put files on that volume. I don't think changing the volume choose config and then compacting will fix this. I think the best option is to run init carefully as you mentioned and/or look into fixing #1373. For 2.1.0 this is fixed by #1389[1] and choices are no longer sticky. So in 2.1, you should be able to change config and then compact. Another option for 2.0 and earlier would be to perform surgery on Accumulo's metadata, but this would be tricky for the root tablet. The following is speculation on what needs to be done. For the metadata table, you could change the srv:dir entries stored in the root tablet (then restart and compact metadata table). For the root tablet itself, you would need to change its dir entry in zookeeper AND move its files to the location specified in zookeeper (doing all of this while Accumulo is down). Accumulo has an admin utility to do this type of thing (it was removed in #1389), but I looked at that utility and its really only suited for user tables and not the metadata or root table. We could possibly make that utility support the metadata and root tables, make it know how to do the surgery I mentioned. [1]: https://github.com/apache/accumulo/pull/1389 > > Many thanks > > Regards, > Karthick
