# Suboptimal Storage Configuration for DocumentDB Cluster Canonical: https://www.pointfive.co/efficiency-hub/inefficiencies/suboptimal-storage-configuration-for-documentdb-cluster Starting with Amazon DocumentDB 5.0, instance-based clusters can use one of two storage configurations. By: PointFive Updated: 2026-09-28 [Cloud Efficiency Hub](https://www.pointfive.co/efficiency-hub) The short version Starting with Amazon DocumentDB 5.0, instance-based clusters can use one of two storage configurations. PointFive Research Cloud cost research at PointFive AWS service [AWS DocumentDB](https://www.pointfive.co/efficiency-hub/cloud-services/aws-documentdb) Category [Databases](https://www.pointfive.co/efficiency-hub/service-category/databases) Reference CER-0376 Type Inefficient Configuration ## Explanation Why the waste happens and who it affects. Standard storage bills I/O on a pay-per-request basis on top of instance and storage charges, while I/O-optimized storage removes I/O charges in exchange for higher instance and storage rates. AWS's guidance is that standard storage suits clusters whose I/O costs are below 25 percent of total cluster cost, and I/O-optimized offers better price performance when I/O costs exceed 25 percent. Clusters keep whichever configuration they were created with unless someone changes it, so I/O-heavy clusters, for example those with working sets larger than the buffer cache, frequent collection scans or heavy write workloads, often keep paying large and variable I/O charges on standard storage. The opposite also happens: light clusters switched to I/O-optimized for predictability pay the higher instance and storage rates without enough I/O to offset them. ## Billing model The pricing dimensions that drive this cost. Standard storage Instance and storage charges plus I/O billed per million requests, so costs vary with workload I/O-optimized storage No I/O charges, with higher instance and storage prices for predictable monthly cost 25 percent guideline AWS suggests I/O-optimized when I/O exceeds about 25 percent of total cluster cost Switching limits A cluster can move to I/O-optimized once every 30 days and back to standard at any time, with no downtime ## How to detect 5 checks to find it in your estate. - Tag DocumentDB clusters, activate cost allocation tags, and use Cost Explorer to break each cluster's cost into instance, storage and I/O to see the I/O share, as AWS recommends for this decision - Chart the VolumeReadIOPs and VolumeWriteIOPs metrics (AWS/DocDB), which report billed cluster volume I/O, to see I/O volume trends per cluster - Flag standard-storage clusters on DocumentDB 5.0 or later where I/O is consistently above about 25 percent of cluster cost - Flag I/O-optimized clusters where modeled I/O at standard rates would stay well below 25 percent of cluster cost - Note clusters on engine versions earlier than 5.0, which do not offer I/O-optimized storage and would need an upgrade first ## How to fix 5 ways to remove the waste. - Switch I/O-heavy clusters to I/O-optimized with modify-db-cluster --storage-type iopt1 or in the console; the change needs no downtime or reboot - Switch light clusters back to standard storage, which is allowed at any time - Before moving a cluster to I/O-optimized, confirm the analysis covers a representative period, because the next move to I/O-optimized is blocked for 30 days; describe-db-clusters shows when the next change is allowed - Reduce I/O itself where possible, for example with indexes that avoid collection scans or an instance size whose buffer cache fits the working set, and re-run the comparison afterwards - Review storage configuration periodically, since workload changes can move a cluster across the 25 percent threshold ## Documentation Vendor references for pricing and configuration. - [Amazon DocumentDB cluster storage configurations docs.aws.amazon.com](https://docs.aws.amazon.com/documentdb/latest/developerguide/db-cluster-storage-configs.html) - [Amazon DocumentDB Pricing aws.amazon.com](https://aws.amazon.com/documentdb/pricing/) - [Monitoring Amazon DocumentDB with CloudWatch docs.aws.amazon.com](https://docs.aws.amazon.com/documentdb/latest/developerguide/cloud_watch.html) ## Related inefficiencies [Browse the library](https://www.pointfive.co/efficiency-hub) - AWS DocumentDB CER-0375 ### [Inactive DocumentDB Cluster](https://www.pointfive.co/efficiency-hub/inefficiencies/inactive-documentdb-cluster) Amazon DocumentDB instance-based clusters bill every instance for each second it runs, whether or not any client is connected, and storage, I/O and backup storage are billed on top. Clusters created to evaluate DocumentDB, to rehearse a... Databases - Databricks CER-0332 ### [Missing Partition Pruning in Delta Lake Table Queries](https://www.pointfive.co/efficiency-hub/inefficiencies/missing-partition-pruning-in-delta-lake-table-queries-on-databricks) When Delta Lake tables are partitioned by specific columns - such as date, region, or tenant identifier - the query engine can use partition pruning to limit data scans to only the relevant subset of files. However, when queries against... Databases - AWS RDS CER-0322 ### [Non-Production RDS SQL Server Using Standard or Enterprise Edition Instead of Developer Edition](https://www.pointfive.co/efficiency-hub/inefficiencies/non-production-rds-sql-server-using-standard-or-enterprise-edition-instead-of-developer-edition) Amazon RDS for SQL Server uses a License Included pricing model where the hourly instance rate bundles Microsoft SQL Server licensing fees on a per-vCPU basis. When non-production workloads - such as development, testing, staging, QA, or... Databases --- Source: the public page above. Product screenshots and illustrative interfaces are examples, not live customer data.