Splunk automatically creates buckets as needed. You don't need to do anything about buckets for a 2TB index; this is not considered a particularly large index in Splunk. (There are customers who add much more than 2TB every day.)
However, you do need to change the maximum size of your index, as the default maximum size is 500,000MB (or .5TB) You can change this setting in the configuation file indexes.conf (maxTotalDataSizeMB) or you can do it via the user interface in the Splunk Manager.
Contrary to wdhathaway's post - a Splunk index is not implemented as a monolithic file; it is in fact a number of files. But I don't think that you will have a significant fsck problem anyway.
FInally, for more about indexes and sizing take a look at
Managing Indexes
Create and edit indexes
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