Recently I migrated one of our indexers to a new machine.
Sometimes searches result in the below message despite there being plenty of space in the /opt/splunk mount and the minFreeSpace being set to 2000 in /opt/splunk/etc/system/local/server.conf.
Dispatch Command: The minimum free disk space (18446744073709551615MB) reached for /opt/splunk/var/run/splunk/dispatch dispite [diskUsage]minFreeSpace = 2000
Well 18446744073 petabytes is a lot for just one indexer. I'd spread it out across... two indexers
run a btool to check where is that config coming from. still its weird since you have the config in system/local
/opt/splunk/bin/splunk btool server list --debug disk
Also which Splunk version are you using?
Found the problem: the /opt/splunk/var/run/splunk/dispatch dir was a symlink to a different storage array on the old machine, and was broken when rsync-ing from the the old host to the replacement, which has a single large /opt/ mount for splunk. Deleting the broken symlink and making a proper dir and then copying data again from the original host cleared up the errors.