HP P4000 SAN Technical White Paper page 11

Estimated time to copy
Link speeds are commonly listed in Mb/s or Kb/s on lower-bandwidth connections. To estimate the time needed for
a copy:
1. First convert the size of the volume to bytes: Begin by multiplying the gigabytes by 1024 to get megabytes.
2. Multiply megabytes by 1024 to get to kilobytes.
3. Multiply kilobytes by 1024 to get bytes.
4. Multiply the bytes by 8 to yield the number of bits.
5. Divide the number of bits by 1000 to yield kilobits or again by 1000 to yield megabits.
6. Finally, divide your result by the link speed to get the number of seconds to complete the copy. Convert to the
correct order of magnitude, Kb or Mb, before dividing by the corresponding units per second of link speed.
Table 3 illustrates the calculation and provides an example.
Table 3. Calculating the estimated copy time.
GB to MB MB to KB KB to bytes
GB MB KB
x 1024 = x 1024 = x 1024 =
MB KB bytes
10 GB 10,240 MB 10,485,760
x 1024 = x 1024 = KB
10,240 MB 10,485,760 KB x 1024 =
10,737,418,
240 B
After determining the amount of time per each remote copy task, you can develop a schedule. Be sure to verify that
the actual times fit your proposed schedules.
Use bandwidth resources
You can employ quality of service (QoS) technologies to limit the amount of bandwidth your remote copy tasks have
available to them. This will ensure that remote copy does not steal bandwidth from other applications.
Understanding your link utilization is important when planning your implementation. Table 4 shows estimated time for
duplicating 10 GB of data to a remote site at various link speeds or bandwidth allocations.
Table 4. Sample data copy times
Link speed
384 Kb/s
768 Kb/s
1.05 Mb/s
1.27 Mb/s
1.54 Mb/s
2.0 Mb/s
3.0 Mb/s
10.0 Mb/s
25.0 Mb/s
500 Mb/s
830 Mb/s
Bytes to bits Bits to Kb
Bytes Bits
x 8 = /1000 =
bits Kb
Example: estimating time for copying 10 GB of data over a 1.05 MB/s link.
10,737,418, 85,829,345,
240 B 920 b
x 8 = /1000 =
85,899,345, 85,899,345
920 b Kb
Remote copy bandwidth
46 KB/s
93 KB/s
128 KB/s
155 KB/s
188 KB/s
244 KB/s
366 KB/s
1220 KB/s
3052 KB/s
61035 KB/s
101376 KB/s
Mb to
seconds to
Kb to Mb copy
Kb Mb/
/1000 = link speed =
Mb seconds (sec)
to copy
85,899,345 85,800
Kb Mb
/1000 = /1.05 Mb/s
85,899 Mb = 81,808 s
Estimated time to copy 10 GB
62 hours
31 hours
23 hours
19 hours
15 hours
12 hours
8 hours
2.5 hours
1 hour
3 minutes
2 minutes
Seconds to Minutes to
minutes to hours to
copy copy
S to copy Min to copy
/60 = minutes /60
(min) = hours (hrs)
to copy to copy
81,808 s 1,363 min
/60 = /60 =
1,363 min 22.7 hrs
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