Calculating the number of overwrite passes for flash drives

Because of the way space is allocated in flash drives, 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, you need to calculate the number of times the system must overwrite the volume with dummy data.

Before you begin

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

Procedure

  1. Select an LDEV on the LDEVs tab in the Logical Devices window, and write down its capacity and the amount of data in the RAID configuration.

    Examples of amounts of data in a RAID configuration:

    n of RAID5(nxD + 1P)

    n of RAID6(nxD + 2P)

  2. Use the following formula to calculate the number of times to overwrite the data (N):

    N = (User-capacity-for-Data x 2) / Capacity-of-target-volume

    When the capacity of the flash drive is 400 GB, 400 GB x n

    Example: The capacity of the flash drive 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 data six times.

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