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MongoDB disk space depends on where the database runs and what “space” you are measuring. Atlas Core can expand attached storage, Atlas Infinite grows within a configured maximum, and self-managed WiredTiger may keep deleted-document space available for reuse without returning it to the operating system. Start by identifying the deployment and the node or partition under pressure; then choose capacity growth, cleanup, or reclamation accordingly.
How can I check disk space on my MongoDB server?
Identify the deployment and affected storage
First establish whether the deployment is Atlas Core, Atlas Infinite, or self-managed. Record the MongoDB version, topology, hosting provider, configured disk capacity, and the node or partition showing pressure. Storage behavior and recovery options differ across these deployment types.
Read trends and performance together in Atlas
In Atlas, review free and used space over time, not just a single snapshot. For Atlas Core, check disk usage alongside IOPS, latency, queue depth, and throughput: a system can have capacity remaining while suffering from a disk-performance bottleneck. MongoDB says Atlas database metrics are collected every 20 minutes by default, though the collection frequency can be changed. Atlas UI disk labels use GB, while usage metrics use GiB, so the displayed numbers may not match one-for-one. See MongoDB’s Atlas metrics documentation.
Compare collection statistics with filesystem capacity
On a self-managed WiredTiger deployment, compare filesystem free space with database and collection statistics. MongoDB recommends db.collection.stats(); its WiredTiger statistics include wiredTiger.block-manager.file bytes available for reuse, which indicates empty space available for reuse. Logical document size, allocated storage, reusable internal space, and filesystem free space are different measurements and need not change together. See MongoDB’s storage FAQ.
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Find what is consuming the volume
Determine whether growth comes from new data, indexes, retained operational data, backups or logs stored on the same volume, or a migration or bulk write. Do not assume the database files are the only consumers: verify what is actually on the pressured host and volume. Sudden migrations and high-speed writes are specifically relevant to Atlas expansion because growth can outpace scaling.
Why is MongoDB disk space not going down after deleting documents?
On self-managed WiredTiger, deleting documents does not necessarily shrink the database files or increase operating-system free space. MongoDB explains that “The WiredTiger storage engine maintains lists of empty records in data files as it deletes documents.” WiredTiger can reuse those records for later writes, but does not ordinarily return that space to the OS just because documents were deleted.
This explains why collection data can fall while allocated files stay large and filesystem free space stays low. MongoDB’s manual describes checkpoints at 60-second intervals; that is a snapshot-writing cadence, not a promise that deleted data will be reclaimed after 60 seconds. Use the reusable-space statistic from db.collection.stats() to help distinguish internal space available for reuse from space actually free on the filesystem.
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MongoDB documents compact and resyncing a replica-set member as ways to defragment and release space. Dropping a collection or index frees the disk space it occupies. These are different operations with different effects; deleting selected documents is not equivalent to dropping an entire collection or index.
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Choose the right remedy for the deployment
| Deployment | Storage behavior | Operator decision |
|---|---|---|
| Atlas Core | Per-node attached disk with storage auto-scaling; tier scaling may also be needed. | Check alerts, scaling state and limits, growth rate, and whether to increase storage or tier. |
| Atlas Infinite | Storage grows with data but is bounded by a configured maximum. | Set and monitor the maximum; writes are blocked when the limit is reached. |
| Self-managed WiredTiger | The operator controls the filesystem; deleted data may remain as internally reusable space. | Compare filesystem free space with collection statistics; assess cleanup, compaction or resync, and added capacity. |
These are materially different storage models, not interchangeable settings. MongoDB documents the Atlas distinction in its storage auto-scaling documentation and self-managed reclamation behavior in its storage FAQ.
For Atlas Core, check scaling before changing data
MongoDB’s current Atlas documentation says Core storage auto-scaling is enabled by default and triggers when any node reaches 90% disk utilization. For AWS, Azure, and GCP, expansion aims toward 70% utilization. Scaling is upward automatically; reducing storage is a separate manual action. Atlas can scale the tier and storage in parallel if the current tier cannot support the larger disk. A scaling operation can temporarily prevent another manual or automatic disk-scaling operation.
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Auto-scaling is not a guarantee that a sudden write burst will be absorbed in time. Review whether auto-expansion is enabled, whether a cluster storage maximum or tier limit has been reached, and whether growth is faster than expansion. MongoDB’s Atlas disk-space alert guidance identifies these conditions and recommends increasing storage or moving to a larger tier when appropriate. For a planned migration or bulk load, arrange sufficient capacity ahead of the burst rather than relying on reactive expansion.
For Atlas Infinite, manage the configured maximum
Atlas Infinite grows with data under a different storage model from Atlas Core attached-disk scaling. Growth is still bounded by the configured maximum; Atlas blocks writes when that limit is reached. Monitor the limit and make sure it matches expected data growth rather than assuming storage can expand without a ceiling.
For self-managed WiredTiger, distinguish cleanup from reclamation
Remove data or indexes only when they are no longer needed. If deletion has already left reusable WiredTiger space, determine whether compaction or replica-set member resync is appropriate for the specific deployment and MongoDB version. Compaction is not an instant, risk-free, universal fix: check the version-specific command documentation and operational procedures before running it. MongoDB also documents autoCompact for Atlas dedicated clusters running MongoDB 8.0 or later; it requires the autoCompact privilege, runs in the background, and should be run on each intended node. Confirm current support and permissions in the Atlas storage FAQ.
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If the workload still needs the space, add capacity rather than expecting deletion or compaction to solve an ongoing growth problem. MongoDB’s alert guidance supports increasing storage as a response, but the correct host-level capacity change depends on the self-managed environment.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should I do when MongoDB disk space is full?
Atlas Core: check the alert and capacity limits
The Atlas condition “Disk space % used on Data Partition” is configurable and defaults to 90% of configured storage. The alert can reflect disabled auto-expansion, growth faster than expansion, or a cluster storage maximum. Check scaling state and cluster-tier limits, then increase storage or move to a larger tier if needed.
Atlas Core also has documented write-blocking behavior at critically low free space on a primary. The thresholds depend on disk size and are Atlas behavior, not universal MongoDB server limits:
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| Atlas Core disk size | Writes block below | Writes unblock above |
|---|---|---|
| 8–20 GiB | 600 MiB free | 900 MiB free |
| 20 GiB–1.25 TiB | 4% free | 6% free |
| 1.25 TiB or more | 50 GiB free | 75 GiB free |
MongoDB notes that deletes can temporarily increase used space, so deleting records during a critical-space incident may not immediately relieve pressure. Review the current Atlas write-blocking documentation for the documented behavior.
Atlas Infinite: check the logical data limit
For Atlas Infinite, identify whether the configured maximum has been reached. Atlas blocks writes at that logical data limit, rather than following Atlas Core’s attached-disk thresholds. Address the configured limit and capacity plan for this deployment model.
Self-managed: establish whether the problem is capacity or reclaimable space
Check actual filesystem free space, identify what shares the volume, and compare that reading with MongoDB collection statistics. If the space is internal WiredTiger space available for reuse, assess compaction or replica-set member resync under version-specific operational guidance. If the workload’s required data still exceeds available disk, arrange more capacity; cleanup alone cannot make continuing growth sustainable.
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