Mirroring operation On system power-up — e.g., at initial installation or whenever a drive is replaced — the M3 will first verify that each drive is an ESI-formatted drive. If so, it then will transfer all data from the primary drive to the mirroring drive. This process can take anywhere from a few minutes to one hour, depending on system activity, amount of voice message storage, and configuration. System operation won’t be affected during the data transfer, because this transfer will occur only when call-processing is making no disk drive access requests. If a primary drive is replaced, data will be copied in the same fashion from the mirror drive to the new primary drive. Again, the replacement drive must be a new, unprogrammed ESI drive. If it’s not, the system may copy all data in the wrong direction — i.e., from the new (mostly empty) primary drive to the mirror drive! Therefore, ESI recommends that the mirror drive be moved to the primary drive mounting position and the new drive be mounted on the mirror drive mounting position.