See “Enabling encryption using key servers” on page 265 for instructions on how to enable  encryption using key servers as the sole encryption key provider. Note:  The system needs at least three USB flash drives to be present before you can  enable encryption using this encryption key provider. IBM USB flash drives are preferred,  although other flash drives might work. You can use any USB ports in any node of the  cluster. Using USB flash drives as the encryption key provider requires a minimum of three USB flash  drives to store the generated encryption keys. Because the system will attempt to write the  encryption keys to any USB key inserted into a node port, it is critical to maintain physical  security of the system during this procedure. While the system enables encryption, you are prompted to insert USB flash drives into the  system. The system generates and copies the encryption keys to all available USB flash  drives. Ensure that each copy of the encryption key is valid before you write any user data to the  system. The system validates any key material on a USB flash drive when it is inserted into  the canister. If the key material is not valid, the system logs an error. If the USB flash drive is  unusable or fails, the system does not display it as output.  If your system is in a secure location with controlled access, one USB flash drive for each  canister can remain inserted in the system. If there is a risk of unauthorized access, then all  USB flash drives with the master access keys must be removed from the system and stored  in a secure place. Securely store all copies of the encryption key. For example, any USB flash drives holding an  encryption key copy that are not left plugged into the system can be locked in a safe. Similar  precautions must be taken to protect any other copies of the encryption key that are stored on  other media. Notes:  Generally, create at least one additional copy on another USB flash drive for  storage in a secure location. You can also copy the encryption key from the USB drive and  store the data on other media, which can provide additional resilience and mitigate risk that  the USB drives used to store the encryption key come from a faulty batch.  Every encryption key copy must be stored securely to maintain confidentiality of the  encrypted data. A minimum of one USB flash drive with the correct master access key is required to unlock  access to encrypted data after a system restart such as a system-wide reboot or power loss.  No USB flash drive is required during a warm reboot, such as a node exiting service mode or  a single node reboot. The data center power-on procedure needs to ensure that USB flash  drives containing encryption keys are plugged into the storage system before it is powered  on. During power-on, insert USB flash drives into the USB ports on two supported canisters to  safeguard against failure of a node, node’s USB port, or USB flash drive during the power-on  procedure. Chapter 7. Configuring settings  261 Enabling encryption using USB flash drives