In the past, I knew indexed data was kept after upgrading a Splunk server from this site.
However, I cannot find that information now.
If you know the Splunk documentation link/URL where this is described, please let me know.
Assuming your Splunk instance is a single standalone server and you didn't move the default location, then yes your indexed data will be under
$SPLUNK_HOME/var/lib/splunk/<your_index>
after a Splunk upgrade.
Under each index will be db, colddb, datamodel_summary, etc. (and describing those is beyond the scope of this question, but you can learn more about it here: http://docs.splunk.com/Documentation/Splunk/6.2.2/Indexer/HowSplunkstoresindexes ).
http://docs.splunk.com/Documentation/Splunk/6.2.2/Indexer/HowSplunkstoresindexes
It is written on above site about indexed data after upgrade?
What I want to know is that to guard old indexed data after splunk server upgrade.
For guarantee, I want to know official answer on Splunk site.
General info: http://docs.splunk.com/Documentation/Splunk/6.2.2/Installation/HowtoupgradeSplunk
Specific info: If you really want to know then open up the installer file (tgz, rpm, etc.) and see exactly which files Splunk will override. You'll see that it doesn't overwrite or delete any of your indexed data at $SPLUNK_HOME/var/lib/splunk/.