Run all three schemes and measure the restore cost of each

short · 45 min · Objective 4.3

Task

Perform full, incremental and differential backups of the same data on the guest, then restore from each and measure what it took. The arithmetic is simple and the point only lands once you have restored from a five-member incremental chain.

Steps

  1. Create a data set of at least 200 MB on the guest and record its size and file count in lab/schemes/data.txt.
  2. Take a full backup, then change some files each day for five simulated days, taking an incremental each time. Record each in lab/schemes/incremental.csv with header day,type,size_mb,duration_sec.
  3. Revert, repeat with differentials, and record in lab/schemes/differential.csv using the same header.
  4. Restore to a fresh location from each scheme, and record in lab/schemes/restore.csv with header scheme,sets_needed,duration_sec,files_correct.
  5. Write lab/schemes/notbackup.md explaining why a snapshot, a synchronised folder and a redundant array are each not a backup, with the single test that disposes of all three.

Verify

grep -c . lab/schemes/data.txt
awk -F, 'NR>1 && NF>=4 {n++} END {print n" incremental run(s)"}' lab/schemes/incremental.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" differential run(s)"}' lab/schemes/differential.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" restore(s) measured"}' lab/schemes/restore.csv
awk -F, 'NR>1 {print $2}' lab/schemes/restore.csv | sort -u | wc -l
grep -Eic 'same (disk|storage)|independent copy|separate' lab/schemes/notbackup.md

Five runs of each scheme, restores measured from each, and at least two distinct set counts across the restores. If the incremental and the differential restore needed the same number of sets, one of the two backup chains was not what you think.

Notes

The single test that disposes of snapshot, sync and redundant array: if it fails when the original storage fails, it is not a backup. It is worth being able to state in one sentence, because it is the answer to a family of exam questions.

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