When erasing external USB drives, follow below recommendations to prevent any issues during the erasure process.

1. Erasure options:
   • Generally speaking, USB external drives consist of SATA drives within a case, the communication with the machine is performed through an internal USB-to-SATA adapter. Most adapters can pass read/write commands to the SATA drive but cannot pass properly firmware commands. Therefore, erasure standards such as "NIST 800-88 Purge" or "Blancco SSD Erasure" tend to fail on these devices. It is advised to erase these drives using normal overwriting standards as well as to disable the erasure options "Enforce Blancco SSD method on SSDs", "Erase remapped sectors" and "Remove hidden areas".
2. Report backup:
   • Whenever erasing several drives in an erasure station, it is always recommended to enable the "Automatic report backup" feature (via the Drive Eraser Configuration Tool) to store immediately the report of any completed erasure.
3. Drive batches:
   • It is advised to erase batches of USB drives having similar capacities and manufacturer. Having batches of drives of similar sizes will ensure that they are processed roughly at the same time.
   • Also, erase USB 2.0 drives in different batches than USB 3.0 drives.
4. Do not hurry to refresh (applicable only if the hotswap feature is enabled):
   • When connecting a new drive, wait for a few seconds (5-10) before pressing the "Refresh drive list" button. This will allow the system to detect the drive properly before it is displayed in the UI.
   • In addition, if you don't see your newly connected drive after refreshing the list, do not rush into pressing the button again: some drives are slower than others and the detection can take up to a few minutes (on rather rare occasions).
5. Refresh frequency (applicable only if the hotswap feature is enabled):
   • You can disconnect a drive, connect a new one then press the "Refresh drive list" button. However, the drive detection/display is faster if you refresh the drives after connecting/disconnecting a drive (e.g. disconnect -> refresh -> connect -> refresh).
6. USB hubs:
   • If you use USB hubs, make sure that they are powered hubs. Keep in mind that erasing N USB drives connected to a hub will divide the erasure speed by N approximately. Therefore, it is advised not to use USB hubs but to connect directly the drives to the USB ports of the machine.
7. Simultaneous erasures:
   • It is recommended not to erase more than 8 drives simultaneously. The maximum amount of drives you can erase also depends on your machine/erasure station specifications (processor, RAM, Motherboard, number of native USB ports, etc.).
8. It is always recommended to use anti-static wrist strap to prevent electrostatic discharges (which can be a cause of hardware failures).

Some additional information about the erasure of external hard drives can be found from this knowledge base article: Erasing external hard drives (USB, eSATA, firewire) and external drive docking stations