Before You Begin

• Read the Cloudera Manager 5 Release Notes.
• Make sure there are no Oozie workflows in RUNNING or SUSPENDED status; otherwise the Oozie database upgrade will fail and you will have to reinstall CDH 4 to complete or kill those running workflows.
• Run the Host Inspector and fix every issue.
• If using security, run the Security Inspector.
• Run hdfs fsck / and hdfs dfsadmin -report and fix any issues.
• If using HBase:
  • Run hbase hbck to make sure there are no inconsistencies.
  • Before you can upgrade HBase from CDH 4 to CDH 5, your HFiles must be upgraded from HFile v1 format to HFile v2, because CDH 5 no longer supports HFile v1. The upgrade procedure itself is different if you are using Cloudera Manager or the command line, but has the same results. The first step is to check for instances of HFile v1 in the HFiles and mark them to be upgraded to HFile v2, and to check for and report about corrupted files or files with unknown versions, which need to be removed manually. The next step is to rewrite the HFiles during the next major compaction. After the HFiles are upgraded, you can continue the upgrade. To check and upgrade the files:
    1. In the Cloudera Admin Console, go to the HBase service and run Actions > Check HFile Version.
    2. Check the output of the command in the stderr log.
       Your output should be similar to the following:

       Tables Processed:
       hdfs://localhost:41020/myHBase/.META.
       hdfs://localhost:41020/myHBase/usertable
       hdfs://localhost:41020/myHBase/TestTable
       hdfs://localhost:41020/myHBase/t
       
       Count of HFileV1: 2
       HFileV1:
       hdfs://localhost:41020/myHBase/usertable /fa02dac1f38d03577bd0f7e666f12812/family/249450144068442524
       hdfs://localhost:41020/myHBase/usertable /ecdd3eaee2d2fcf8184ac025555bb2af/family/249450144068442512
       
       Count of corrupted files: 1
       Corrupted Files:
       hdfs://localhost:41020/myHBase/usertable/fa02dac1f38d03577bd0f7e666f12812/family/1
       Count of Regions with HFileV1: 2
       Regions to Major Compact:
       hdfs://localhost:41020/myHBase/usertable/fa02dac1f38d03577bd0f7e666f12812
       hdfs://localhost:41020/myHBase/usertable/ecdd3eaee2d2fcf8184ac025555bb2af

       In the example above, you can see that the script has detected two HFile v1 files, one corrupt file and the regions to major compact.
    3. Trigger a major compaction on each of the reported regions. This major compaction rewrites the files from HFile v1 to HFile v2 format. To run the major compaction, start HBase Shell and issue the major_compact command.

       $ bin/hbase shell
       hbase> major_compact 'usertable'

       You can also do this in a single step by using the echo shell built-in command.

       $ echo "major_compact 'usertable'" | bin/hbase shell

• Review the upgrade procedure and reserve a maintenance window with enough time allotted to perform all steps. For production clusters, Cloudera recommends allocating up to a full day maintenance window to perform the upgrade, depending on the number of hosts, the amount of experience you have with Hadoop and Linux, and the particular hardware you are using.
• To avoid generating many alerts during the upgrade process, you can enable maintenance mode on your cluster before you start the upgrade. Be sure to exit maintenance mode when you have finished the upgrade, in order to re-enable Cloudera Manager alerts.

Continue reading:

• Upgrading from CDH 4 to CDH 5 Parcels
• Upgrading from CDH 4 Packages to CDH 5 Packages