Suppose i have a storage array of size 1 petabytes. And i want to replicate it to another storage array, may be for backup purposes.
What i want to know is,
the things that I have to keep in mind while calculating the time,
the things that will effect the time taken for transfer,
and may be an idea of the time taken.
Your effective transfer rate will depend on the speed of the disk and the speed of the network. The slowest part will determine the effective speed. If you can saturate 4 10Gb/s ethernet links, you can get 18 TB per hour transferred. That would mean about 57 hours for a full sync.
That is uncommonly fast, though- backups at a file level tend to be limited by the memory and CPU needed to enumerate the files. You haven't provided enough information to be in any way specific. What kind of array? What kind of backup?
amount of data to transfer
transfer time = ---------------------------- * Overhead_correction_factor
The transfer speed is the lower limit of:
- your ability to read data from the source
- the maximum write speed at the destination
- the speed of the medium connecting the source and destination and the protocol you use.
The Overhead_correction_factor is often set at 110% i.e. to transmit 100MB of actual data you'll actually need to transfer 110MB down the wire where the additional 10% is protocol overhead, the header in each an every TCP packet, sequence numbers, encoding etc.
There are a number of calculators such as http://techinternets.com/copy_calc that will do the unit conversions and calculations for you.
If your source data is also subject to changes those changes will also need to be replicated, increasing your sync time.
Storage arrays often replicate at block level, at the worst case you'll need to replicate 100% of the raw capacity, rather than the amount of actual data stored on the array.