Hello
I thought of different ways of integrity check for the backup and look for the fastest approach to start programming.
in all these approaches randomness is used.
I would appreciate if someone give more suggestions or correct me.

1- Machine Name Check We can check if the machines were backed up.
• Randomness should not be used in this approach.
Advantage:
- Easy to implement
- quick
Disadvantage:
- ???

2- Timestamp
Timestamp on the file and directories will be checked to be sure if they are the same. This approach needs to compare the timestamp in the file system with the timestamp of a specific file which is stored in the backup. Timestamp is stored in the file system table, so one can look and figure out what the last modified timestamp for a certain file is.
Advantage:
- Easy to implement
- Need not to restore any Data
Disadvantage:
- The content can not be checked

3- Size
Advantage:
- Need not to restore any Data
- Fast Approach
Disadvantage:
- The content can not be checked. two files can have a same size, but two different content

4- Checksum
Advantage:
??
Disadvantage:
- Files need to be restored
- Collision may happen

5- Comparing Byte by Byte
Byte-by-byte comparison of files means that the contents of two files to be compared, is read byte-by-byte (in parallel) and checked for equality.
The cmp utility compares two files of any type and writes the results to the standard output. By default, cmp is silent if the files are the same; if they differ, the byte and line number at which the first difference occurred is reported.
cmp –l file1 file2
Advantage:
- 100% accurate
- Fast as it does less calculation
Disadvantage:
- Expensive for the big files
- Files need to be restored

and I also have a question:
what are the advantages and disadvantages of doing randomness in comparing?

Thanks