Performance is not critical for external drives used only for archiving, as file copies are not constrained by the demands of real time recording and playback. First, see if the drive qualifies as a candidate for evaluation by using the rule of thumb calculation provided below. Next, evaluate the drive in real recording, playback, and editing scenarios. Playback of edited cuts assigned to hot-keys is a good test. Audio should never drop out or skip.
Recording is another good test since some drives take longer to write than read.
To consider a drive for qualification testing the result of this calculation should be less than 100. Hard drives rank high in reliability. Removable media tend to have lower reliability because of the additional handling and exposure to the elements. Multiple units must be tested for weeks in playback, editing, archive, and recording scenarios to determine whether a drive is reliable enough for use in a critical, professional application. Compare drive reliability specifications to those of high quality hard drives as a starting point for choosing candidates for evaluation as an external drive.