Modify Range Size in a Sharded Cluster

The default range size for a sharded cluster is 128 megabytes. This default range size works well for most deployments; however, if you notice that automatic migrations use more I/O than your hardware can handle, you may want to reduce the range size. A small range size leads to more rapid and frequent migrations. The allowed size is between 1 and 1024 megabytes, inclusive.

To modify the range size, use the following procedure:

Connect to any mongos in the cluster using mongosh.
Issue the following command to switch to the Config Database:
```
use config
```
Issue the following command to store the global range size configuration value:
```
db.settings.updateOne(
   { _id: "chunksize" },
   { $set: { _id: "chunksize", value: <sizeInMB> } },
   { upsert: true }
)
```

Modifying the chunk size has several limitations:

Starting in MongoDB 6.0.3, automatic chunk splitting is not performed. This is because of balancing policy improvements. Auto-splitting commands still exist, but do not perform an operation. For details, see Balancing Policy Changes.
Starting in MongoDB 6.0, the following auto-splitting commands do not perform an operation:
- sh.enableAutoSplit()
- sh.disableAutoSplit()
In MongoDB versions earlier than 6.0, automatic splitting only occurs for insert or update operations.
If you lower the chunk size, it may take time for all chunks to split to the new size.
Splits cannot be undone.
If you increase the chunk size, existing chunks grow only through insertion or updates until they reach the new size.
The allowed range of the chunk size is between 1 and 1024 megabytes, inclusive.

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Balancer