Is upgrading CDH 4.5 to 4.6 without making changes...
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I've done full stack 4.2.1 to 4.4, and 4.4 to 4.6 rolling upgrades manually with no troubles and minimal impact in the form of retries to the end-users. I don't know that i would try upgrading only to hbase 4.6 while leaving hdfs on 4.5 since that version of hbase won't have been thoroughly tested with the 4.5 version of hdfs. having said that it doesn't look like cloudera pushed many changes to hdfs between 4.5 and 4.6 so i suppose you could try it, let me re-iterate that i don't think i would though.