IBM DS3000 Introduction And Implementation Manual page 205

Draft Document for Review August 30, 2007 12:59 am
When converted, 5 GB equals 5,368,709,120 bytes.
[5 x 1024(K) x 1024(M) x 1024(G)]
2. Divide the base logical drive's capacity (in bytes) by 2000.
When divided, the result is 2,684,354.56 bytes.
3. Convert the result from step 2 (in bytes) to kilobytes (KB).
When converted, the result is 2621.44 KB.
[2,684,354.56 / 1024(K)]
4. Add 192 KB to the results from step 3.
192 KB + 2621.44 KB = 2813.44 KB
5. Convert the result from step 4 to megabytes (MB).
When converted, the amount of management overhead required is calculated to be
2.75 MB (or 0.002686 GB).
6. In this example, 30% of the data blocks on the base logical drive are expected to change.
To accurately calculate the FlashCopy repository logical drive capacity, sufficient space
needs to be allowed for the copy-on-write data as well as the management overhead
(calculated in step 5).
To calculate the copy-on-write space required, calculate the percentage of the base logical
drive expected change:
30 percent of 5 GB = 1.5 GB
The final estimated FlashCopy repository logical drive capacity for this example is:
1.5 GB + 0.002686 GB = 1.502686 GB
7. In the Create FlashCopy logical drive Wizard, you will use this calculated value in the
Repository Capacity window to specify the percentage (%) full box of base logical drive to
set the estimated FlashCopy repository logical drive capacity (see Figure 8-65 on
page 182).
Note: The percentage (%) full box sets the FlashCopy repository logical drive capacity
as a percentage of the base logical drive. Using the percentage (%) full box, increase or
decrease the percentage until the FlashCopy Repository logical drive Capacity value
matches the estimated capacity calculated in step 6. (Some rounding up might be
required.)
FlashCopy failure policy
The FlashCopy repository logical drive's failure policy determines what happens if the
FlashCopy repository logical drive becomes full (that is, all of its capacity has been used).
The choices are:
Fail FlashCopy logical drive:
When the FlashCopy repository logical drive becomes full, the associated FlashCopy
logical drive becomes invalid. This is the default policy. The base logical drive remains
online and user accessible and writable.
Fail writes to base logical drive:
When the FlashCopy repository logical drive becomes full, writes to the base logical drive
fail. The FlashCopy logical drive is preserved and remains valid since no new
copy-on-write data is generated for the FlashCopy repository logical drive.
7065Admin_Configure.fm
Chapter 8. Administration - Configure
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