Getting incremental persist failed from middle manager

We just started getting this error from middle manager.

2016-07-13T12:35:48,957 INFO [sparrow-firehose-web-incremental-persist] io.druid.segment.realtime.plumber.RealtimePlumber - DataSource[sparrow-firehose-web], Interval[2016-07-13T12:00:00.000Z/2016-07-13T13:00:00.000Z], Metadata [null] persisting Hydrant[FireHydrant{index=io.druid.segment.incremental.OnheapIncrementalIndex@289efc97, queryable=io.druid.segment.ReferenceCountingSegment@5dd93256, count=27}]
2016-07-13T12:35:48,957 INFO [sparrow-firehose-web-incremental-persist] io.druid.segment.IndexMerger - Starting persist for interval[2016-07-13T12:00:00.000Z/2016-07-13T13:00:00.000Z], rows[75,000]
2016-07-13T12:35:49,488 INFO [sparrow-firehose-web-incremental-persist] io.druid.segment.IndexMerger - outDir[/tmp/persistent/tasks/index_realtime_sparrow-firehose-web_2016-07-13T12:00:00.000Z_0_0/work/persist/sparrow-firehose-web/2016-07-13T12:00:00.000Z_2016-07-13T13:00:00.000Z/27/v8-tmp] completed index.drd in 0 millis.
2016-07-13T12:35:49,685 ERROR [sparrow-firehose-web-incremental-persist] io.druid.segment.realtime.plumber.RealtimePlumber - dataSource[sparrow-firehose-web] – incremental persist failed: {class=io.druid.segment.realtime.plumber.RealtimePlumber, interval=2016-07-13T12:00:00.000Z/2016-07-13T13:00:00.000Z, count=27}

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I checked the permission of the folder and Druid has access to that folder. I’m not sure what caused this error to happen and how to fix it? Does it mean that I lose 27 events?

Thanks,

Do you have the full stack trace or the task log? Usually there should be more information abut why the persist failed.