# max\_concurrent\_io

Available since NATS Server `2.15`

Hot Reloadable

Only reloadable while JetStream is being disabled in the same reload (the whole `jetstream` block removed or `enabled: false` set). Any other change while JetStream stays enabled fails the reload.

Maximum number of disk I/O operations the server allows in flight at once, across all streams and consumers. Must be between 4 and 8192. Lower it to reduce contention for the underlying disk on a server with many assets; raise it on fast storage to allow more parallel I/O.

## Types

| Type      | Description | Choices |
| --------- | ----------- | ------- |
| `integer` | -           | -       |