Calculating the number of overwrite passes for flash drives or SCMs

Volume Shredder User Guide
Version
9.6.0
Audience
anonymous
Part Number
MK-98RD9018-04

Because of the way space is allocated in flash drives or SCMs, the dummy data that is used to overwrite the volume must exceed the capacity of the target volume. Therefore, before you shred a volume on flash drives or SCMs, you need to calculate the number of times the system must overwrite the volume with dummy data.

You must have the Storage Administrator (Provisioning) role to perform this task.

  1. Select an LDEV on the LDEVs tab in the Logical Devices window, and write down its capacity and the number of data drives in its parity group (for example, 3 drives for RAID5-3D+1P, 6 drives for RAID6-6D+2P).
  2. Use the following formula to calculate the number of times to overwrite the selected LDEV:
    n = [(drive-capacity × number-of-data-drives-in-parity-group) × 2] / LDEV-capacity

    Example: The capacity of the flash drive or SCM is 400 GB, the RAID configuration is 3D+1P, and the LDEV capacity is 440 GB.

    [(400 x 3) x 2 ] / 440 = 5.45 = six times

    Round up the value (5.45) to the nearest whole number. You need to overwrite the LDEV six times.