LUN (VLL) and Volume Shredder User Guide (T5214-96094, November 2011)

Calculating the Number of Shredding Operations Necessary to Overwrite Data in Target Volume

with Dummy Data to Delete

When a flash disk is used, space is newly allocated in response to a write request and the target

volume to delete data is converted to space. For this, data deleting by overwriting data using the

data exceeding the capacity of target volume is required.

Procedures to calculate the number of shredding operations necessary to overwrite data in the

target volume with dummy data are as follows.

1. Confirm the capacity of the target volume for data deleting and the amount of data in the

RAID configuration in the VLL window.

Example: Confirm the amount of data in a RAID configuration.

N of RAID5(nxD + 1P)

N of RAID6(nxD + 2P)

2. Where the number of shredding operations necessary to overwrite data in the target volume

with dummy data is N, it can be calculated using the following formula:

N (rounding up after the decimal point) = (Capacity-of-target-volume + User-capacity-for-data)

/ Capacity-of-target-volume

User capacity for data:

• Example: When the capacity of a flash disk is 72GB, the user capacity for data is 72GB

x n

• Example: When the capacity of a flash disk is 400GB, the user capacity for data is

400GB x n

A sample calculation of the number of shredding operations:

• Sample configuration: Flash disk is 72GB, RAID configuration is 3D+1P, and LDEV is

100GB.

Calculate the number of shredding operations. (72 x 3+100) / 100 = 3.16.

Round up the value 3.16 to the nearest whole number, so dummy data writing must be

performed four times.

• A sample calculation of data-deleting conforming to DoD5220.22-M (performing dummy

data overwriting four times).

Sample configuration: Flash disk is 72GB, RAID configuration is 3D+1P, and LDEV is

100GB

1. Calculate the number of shredding operations:

(72 x 3+100) / 100 = 3.16. Round up the value to the nearest whole number, so

dummy data-writing must be performed four times.

2. Define shredding settings

See “Defining the Shredding Settings” (page 81) to enter dummy data 00 in the text

box and add a row to the Format List (add rows for performing the shredding

operation four times to the Format List).

3. Delete the data in volume.

See “Deleting the Data in the Target Volume” (page 82), and execute the shredding

operation.

4. Perform [2] and [3] using dummy data FF.

5. Perform [2] and [3] using dummy data 00.

Volume Shredder Operations (For Volumes Using Hard Disk) 85