What the blocking factor is
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A tape block is 1,024 bytes of data. During a tape backup or restore, you can specify the number of tape blocks that are transferred in each read/write operation. This number is called the blocking factor.
You can use a blocking factor from 4 to 256. If you plan to restore a backup to a system other than the system that did the backup, the restore system must support the blocking factor that you used for the backup. For example, if you use a blocking factor of 128, the system on which you restore that backup must support a blocking factor of 128.
During an NDMP backup, the MOVER_RECORD_SIZE determines the blocking factor. ONTAP allows a maximum value of 256 KB for MOVER_RECORD_SIZE.