A user of eDiscovery needs to be able to view all of the content that has the potential to be discoverable. It is recommended that you create a security group for the users of eDiscovery. You can grant various levels of permissions to the different security groups rather than to individual users. Select a name for the security group and then record it. You also need to document the security group that each user belongs to.
In SharePoint 2013, users of eDiscovery have to be able to view all of the content. There are a couple of ways that can be done. Grant users of eDiscovery access to all the content in a web application. This can be done by using a web application user policy. Add eDiscovery users as site collection administrators for each site collection that offers discoverable content. It is recommended that you grant permissions at the web application level whenever that is possible in your particular environment.
Since SharePoint Online is a hosted service, the administrators aren’t able to access the web applications directly. With SharePoint Online, you have to add eDiscovery users as site collection administrators on each site collection if it contains discoverable content.
Decide if you will grant permissions by web application or site collection. If you will have to grant permissions at the web application level, then you need to identify which of the web application you will rely on to grant access to eDiscovery users. It is very possible that this will be all of the web applications. If you grant permissions at the site collection level, you need to identify which site collections eDiscovery users will need to have access to and record that information on your worksheet.
Typically, if you export content from eDiscovery, you will also need to export a list of things that aren’t able to be indexed. The search crawl log will contain that information. This means eDiscovery users also have to be able to access the search crawl log.