Advanced indexing of custodian data
When a custodian is added to an Advanced eDiscovery case, any content that was deemed as partially indexed or had indexing errors is reindexed to make it fully searchable. This reindexing process is called Advanced indexing. There are many reasons that content is partially indexed or has indexing errors. This includes image files or the presence of images in a file, unsupported file types, or file sized indexing limits. For SharePoint files, Advanced indexing only runs on items are marked as partially indexed or that have indexing errors. In Exchange, email messages that have image attachments are not marked as partially indexed or with indexing errors. This means that those files will not be reindexed by the Advanced indexing process.
To learn more about processing support and partially indexed items, see:
Viewing Advanced indexing results
After the Advanced indexing process is completed, you can get an understanding of the effectiveness of reprocessing. In the Advanced indexing results view on the Processing tab for a case, the graph lists the number of items added to the hybrid index. The hybrid index is where Advanced eDiscovery stores the reprocessed content.
This view also includes the number of items that require remediation and another graph of errors by file type. For more information, see:
Updating the Advanced index for custodians
When a custodian is added to an Advanced eDiscovery case, all partially indexed items are reprocessed. However, as time passes, more partially indexed items may be added to a user's mailbox or OneDrive account. If necessary, you can update the index for specific custodian. For more information, see Manage custodians in an Advanced eDiscovery case. You can also update the index for all custodians in a case by clicking the Update index on the Processing tab.
Updating custodian indexes is a long running process. It's recommended that you don't update indexes more than once a day in a case.