# Controlling UFS Bandwidth

When Alluxio reads data from an underlying file system (UFS), especially during cache-warming jobs or periods of high cache misses, the traffic can overwhelm the UFS. This can impact other applications that rely on the same UFS. To prevent this, Alluxio allows you to limit the UFS read bandwidth on each worker.

## How It Works

The UFS read rate limiter restricts the maximum bandwidth per second for all UFS reads originating from a single Alluxio worker. While peak bandwidth may occasionally exceed the configured limit for very short bursts, the *average* bandwidth will be capped at the specified rate.

This feature is currently supported for the following UFS connectors:

* HDFS
* Amazon S3
* Google Cloud Storage (GCS)
* Alibaba Cloud OSS
* Tencent COS

## Configuration

To enable the UFS read rate limiter, set the following property in `alluxio-site.properties` on each worker. The value is specified in megabytes per second (MB/s).

```properties
# Limit UFS read bandwidth to 100 MB/s per worker
alluxio.worker.data.ufs.read.rate.limit.mb=100
```

By default, this feature is disabled (unlimited). Setting this property enables the limiter with the specified bandwidth cap.