Index on ingest - MarkLogic Server indexes documents as they're ingested. If your data model and index configuration is where it needs to be, that means your data is ready to be queried as soon as it's in a MarkLogic Server database. If your index configuration isn't quite where you want it, however, revising it means reindexing your entire database, creating lots of obsolete documents and resulting in potentially multiple large merge operations. This is why it's always better in MarkLogic Server to optimize your index settings in smaller environments before propagating those index settings to your bigger environments, and why you'll want to do fewer, bigger index configuration changes instead of many small index configuration changes. Each index configuration change - regardless of size - will trigger a reindex, so you'll want to minimize the number of reindexes you need to perform instead of the minimizing the number of changes in any one reindex.

In addition to reindexing, other aspects of MarkLogic Server that take up significant storage bandwidth include:

• Rebalancing - which redistributes your data across your database
• Local disk failover/database replication - both make copies of your data, and those copies need their own resources
• Backup/restore - backup is making a copy of your data, and restore is effectively a mass update of your data
• Mass updates of existing documents - Because of the way updates are performed in MarkLogic Server (read more), updating a large number of existing records will create a large number of obsolete documents, and consequently result in lots of large merge operations. To help reduce performance overhead, and if you have no need to preserve attributes of your existing data (read more), you might want to consider simply reloading data into an empty database, instead (which would result in avoiding the creation of obsolete documents and consequent merges)

References:

Understanding System Resources
Understanding MarkLogic Minimum Disk Space Requirements
MarkLogic - Lazy Deletes
Mass Updates - "node-replace" vs "document-insert"