NOTE   For HSM firmware version 7.7 and newer, triple-DES keys have a usage counter that limits each key instance to encrypting a maximum of 2^¹⁶ 8-byte blocks of data when the HSM is in FIPS mode (that is, when the "Allow non-FIPS algorithms" policy [12] is set to 0). When the counter runs out for a key instance, that key instance can no longer be used for encryption or wrapping or deriving or signing, but can still be used for decrypting and unwrapping and verifying pre-existing objects.

The CKA_BYTES_REMAINING attribute is available when the Non-FIPS algorithms policy is set to 0, but cannot be viewed if the Non-FIPS algorithm policy is set to 1.

The attribute is preserved during backup/restore using a G7 Backup HSM; restoring puts the counter back to whatever value it had before backup.
The attribute is not preserved through backup/restore using a G5 Backup HSM; restoring sets the counter to like-new state (no usage).