While it may be technically possible in some setups, it is generally not recommended to plug in two external hard drives at once, particularly when using a USB hub or adapter.
The primary concern stems from the power requirements of the drives. External hard drives, especially those that draw all their power directly from the USB port (bus-powered drives), can demand a significant amount of electricity.
Why Connecting Two Drives Can Be Problematic
Connecting two external hard drives simultaneously to a single hub adapter can lead to issues due to an excessive power draw.
- Insufficient Power Supply: USB ports and connected hubs have a limited power output. When two power-hungry devices like external hard drives are connected to the same hub, the combined power demand can exceed the hub's capacity or the port it's connected to.
- Malfunction and Instability: With insufficient power, the hard drives may not function correctly. This can manifest as:
- Unrecognized drives: One or both drives might not show up on your computer.
- Frequent disconnections: Drives might randomly disconnect, leading to data transfer interruptions.
- Slow performance: Data transfer speeds can significantly decrease.
- Data Corruption: Inadequate power during read/write operations can potentially corrupt data on the drives.
- System Overload: In rare cases, continuously drawing too much power could potentially strain the USB controller of your computer, though modern systems have safeguards.
Understanding Power Requirements
External hard drives come in two main types based on their power source:
Type of External Hard Drive | Power Source | Typical Use Case |
---|---|---|
Bus-Powered | Draws power from the USB port | Portable drives, smaller capacities |
Self-Powered | Uses an external AC adapter | Desktop drives, larger capacities |
Bus-powered drives are the main concern when plugging in multiple units, especially via a hub, as they rely entirely on the USB port for power. Self-powered drives, since they have their own power supply, are less likely to cause power issues for the USB port itself, but they still require a data connection.
Best Practices and Solutions for Multiple Drives
If you need to connect multiple external storage devices, consider the following strategies to ensure stability and functionality:
- Use Self-Powered Drives: Whenever possible, opt for external hard drives that come with their own dedicated power adapter. This alleviates the power burden on your computer's USB ports and hubs.
- Utilize Powered USB Hubs: If you must use bus-powered external hard drives, invest in a powered USB hub. Unlike unpowered hubs, a powered hub has its own AC adapter, providing sufficient power to all connected devices.
- Example: A common setup might involve plugging a powered USB 3.0 hub into one of your computer's USB-A ports, then connecting your external drives to the powered hub.
- Direct Connections to Different Ports: If your computer has multiple independent USB-A ports, connecting each bus-powered drive to a separate port directly on the computer can sometimes distribute the power load more effectively than using a single unpowered hub. However, even direct ports have their limits.
- Prioritize Critical Devices: If you only need one drive active at a time, connect only the drive you are actively using to minimize power consumption and potential conflicts.
- Daisy Chaining (with caution): Some specialized external drives (e.g., Thunderbolt enclosures) allow for daisy-chaining, where one drive connects to the computer, and another connects to the first drive. This is typically designed for specific high-bandwidth interfaces and is not common for standard USB hard drives.
In summary, for optimal performance and to avoid potential issues, it is recommended to connect only one external hard drive at a time, especially when relying on a hub adapter, as two will likely require too high of a power draw and may not function correctly.