CISSP Practice question #134

How many backup tapes would we use to restore all the data if we do weekly full backups Sunday at midnight and daily incrementals at midnight and the system fails Wednesday afternoon?
A: 2
B: 3
C: 1
D: 4

CBK 7: Security Operations
Source: practice tests


B: We would need the Sunday full tape, the incremental tapes from Monday and Tuesday night so 3 tapes total.

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    1. Also completely agree with you Marilyn, using less confusing times are used widely because people get confused (even more with AM/PM).
      CISSP is however to some extend not the world you and I work in. There will be questions like this and in the prep is where you want to find out 🙂

    1. Midnight is at 1200am. If the full back up is on midnight on SUNDAY that would be 1 tape. an incremental back up on midnight on MONDAY would be 2 tapes. an incremental back up on midnight on TUESDAY would be 3 tapes. And since the failure happened on WEDNESDAY AFTERNOON, there would be another back up at midnight on WEDNESDAY at 12AM. That would make 4 tapes.

    2. Time can be fascinating. 12 midnight is the night of the day, 12:01am is the next day. 12:01am Sunday morning, would be an incremental backup. Sunday midnight is after 11:59pm Sunday night which is the full backup.

    3. It sucks when ISC2 has bad questions and answers. Hopefully it wouldn’t come down to a single question determining pass/fail, but a test taker in that position should challenge this as a bad question and “correct” answer.

    4. When we use the word “midnight” in common parlance, we refer to the 24 hour period preceeding same. Midnight Sunday refers to the period between Sunday and Monday. I understand how one might be confused, but I’d probably stick to common uses, not uncommon. Therefore, the correct answer as Thor Pedersen laid out, is 3.

    5. That’s because midnight is definitionally the space between day one and day two. The date change you see, philosophically, occurs only *after* midnight.

      Even if you are “right” in some sense, technically, it’s that clock tick from 11:59:59:59… to 12:00 that triggers the chron. In that minute space before 12:00 but after the 11:59 tick that is the triggering event.

      So, if your answer were correct, it would occur *after* that clock tick and not *during.*

      But even if you are correct that the chron trigger occurs after the clock tick, when it *is* for the computer’s purposes, “next day,” then, it is no longer actually midnight and is – at that precise point – “next day.”

      If you would like to discuss the finer points of computer theory, please hit me up.

    6. Mickey Foo actually, I would never start a backup job during this time frame. Most end of day processes need to complete prior to the backup job starting. I usually encourage people to wait and start at any other time than midnight.

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