Good morning. Yes they coexist with no issues. Both v1 and v2 indexing will use the same “Index Cache” directory that is configured in the Catalog tab of the MediaAgent properties.
The retention setting in the “Catalog” tab of the MediaAgent properties is for v1 index only. v2 index retention works differently depending on if it is v2 subclient based indexing or v2 backupset indexing.
It is important to ensure that your index backups which run as “Big Data Apps” jobs are running successfully. If they are not, compaction can not happen and the index can not be physically pruned.
For performance, it is recommended to have the Index on a locally attached SSD. Be sure to follow the sizing recommendations shown here:
https://documentation.commvault.com/11.24/expert/92111_system_and_hardware_requirements_indexing_version_2.html