During monitoring hbase region server logs when major compaction gets initiated, I see sometimes the log says
regionserver60020-smallCompactions-1434465640016] regionserver.HStore: Completed major compaction of 7 file(s) i.....
and sometimes
[regionserver60020-largeCompactions-1434432485236] regionserver.HStore: Completed major compaction of 9 file(s) in
How is this smallCompaction and largeCompaction gets categorised ?
Major compaction speed can very widely as it may perform different subtasks depending on size and number of file, size of memory cache. For instance, it could be performing region splits based on enabled split policy. So it all depends on your write volume, disk speed, hbase configuration, scheduled jobs etc.