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I'm in the process of designing my first ever backup scheme. I'm completely new to managing data backup, and there are some concepts that I don't totally understand. Here's what I've got so far, and what equipment I'll be using.

There are only three servers that I will be backing up, total data is approx 200Gb. I will be doing weekly full backups on Saturdays, followed by differential backups Mon thru Fri nights. There will also be an end of month full backup that will be stored off site for DR purposes.

Equipment being used: -8 slot tape backup drive -LTO2 tapes -Backup Exec 12.5 with Exchange and SQL Agents

I will be using two sets of tapes, the first for Week 1, and then another for Week 2, which will be alternated back and forth every other week.

So my question is this, how many tapes should I be using in each set? Do I have to use eight since the backup drive accepts up to eight tapes? Will it be thrown off if I put less in?

Secondly, since the diff backups each weeknight will probably only be about 5Gb or so at most, do I need to put in five LTO2 tapes (which hold up to 400Gb) into the media pool, one tape for each night? Or is one sufficient, since it could theoretically hold many weeks worth of diffs?

What I don't understand is if BE selects a new tape for each day, or if it will just continue to append to the same tape until it's full and then roll over to the next one.

Perhaps the easier question to ask, is, if you had the backup equipment and servers to backup listed above, what would your backup design be?

Many thanks....

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7 Answers 7

I would highly recommend the book "Backup & Recovery" (O'Reilly Book) by W. Curtis Preston


Asking how to do your backup plan is kinda like asking 10 grandmothers how to make the best chicken noodle soup. You'll get 10 different answers but all of them will agree on the basic ingredients.

In my opinion, Backup & Recovery does a pretty good job of talking about the strengths and weaknesses of different options you may (or may not) choose to implement.

So, that's where I'd start first.

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I'll check it out. Would you be able to answer my question regarding how Backup Exec handles writing data to tapes that are in the same media pool? –  Citizen Chin Jun 14 '09 at 21:17

It's been a while since I set this up, and I'm at home so I'm going from memory.

In our case, we have an LTO-3 drive, a full backup fits on two tapes and all the diffs for a week fit on one. So every week, we have a set of tapes consisting of the two tapes for the full and a third tape for the following 5 diffs. We keep these sets for 5 weeks, we have one set offsite and 4 onsite.

We set up a media pool for the full backups with the overwrite time set to 5 weeks so that the tapes can't be re-used before that and set it to not be appendable so the next time you use a tape it starts at the beginning.

For the diffs, the media pool was set to 1 week, because after that we wouldn't really care about what was on the diffs and if we needed to we could grab a "wrong" diff tape. In practice, as I said, we always keep the set of tapes for the week together. But when we first got the LTO-3, the tapes were $50 and we were thinking we'd save money by only having a couple diff tapes and re-using them.

(I said "was" for the diff media pool because we actually stopped doing the diffs to tape and we now do a similar disk-disk-tape scheme: full backup to disk and then copy that off to tape, then the diffs are only to disk.)

To answer your specific question, when you set up the backups, you tell it which media pool to get a tape from and it'll grab the first one that's usable - that's allowed to be written to.

You said LTO-2 and 200GB, so a full should fit on a couple of your tapes, 3 at the very worst. So you could have 6 tapes for fulls and 2 for diffs in the loader at once, then every week you have to pull out one set of fulls and put in another one. If your backups fit on 2 tapes, you could have 3 sets of fulls and you only have to swap every 2 weeks.

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Thank you for all of the answers thus far, they have been quite helpful. Another question, as I can't seem to find the answer on Symantec's site, what are the 'scan' and 'inventory' functions for? Also, regarding labels, if you don't manually label a tape, will BE assign one to it itself? –  Citizen Chin Jun 15 '09 at 17:59

Backup Exec can be configured to use different slots for the full and incremental backups.

The biggest weakness I see in you plan is two backup sets of tapes. Three sets are considered an absolute minimum. I generally use at least five sets.

You may also consider a monthly full backup that you keep for a year.

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I agree that you need more then 2 backup sets. I consider 4 to be a reasonable number (so you have approximately a months worth of tapes to go back to if something goes haywire). When you set up backups in Backup Exec you have the choice of either appending the data or overwriting the data. You also have a choice of what to do if you said append but the tape is full. In addition you can control the overwrite protection settings on your media pool so you can prevent a tape that was just used from being accidently overwritten. One tip, I tend to find that the tapes don't always get changed when they are supposed to (because someone is out sick, or on vacation or there is a holiday), so if possible I try to have two sets of tapes in the drive. The ones for this week, and the ones for NEXT week. So that you have a full week to pull out the current backups before things get messed up. Also, you should take a look at whether 6 nights of differentials will fit on one tape. If they don't, but 6 nights of incrementals would you might want to consider incrementals. It increases the time it takes to do a full restore (especially towards the end of the week), but it could be worth it if it reduces the number of tapes required.

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As well as tape I would highly recommend taking a disk to disk copy to another server or SAN type device.

Tapes are great for archival purposes, but nothing beats having a local copy on disk for fast, hassle free recoveries.

If you have a WAN, consider sending disk backups off site up the wire. Depending on how much you pay for bandwidth this can be a cost effective way to get multiple copies of your most important data in different locations.

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I don't know how Backup Exec works, but I can answer in general.

The tools I have used can all limit their backup sets to the minimum required number of tapes. What I mean is that if you load 8 blank tapes into your robot, but you only write to the first three, then only those three tapes are part of the backup set. The remaining five are not, and can therefore be used for something else.

Also, these tools can be configured to append to an existing tape if there is space available. So if your daily is 5GB, and your system is configured so, it will append the next day's incremental to the first tape. If your incrementals are really so small, you will end up using two tapes and just rotating between them. Of course, this means you get to worry about media lifetimes as well -- tapes wear out just like everything else.

Second: you have to be careful about the difference between a "differential" and an "incremental" backup. A "differential" backup is all the differences between "now" and a reference point, usually the last full backup. So if your delta is about 5GB a day, then the first day it will be 5GB, the second potentially 10GB, etc, etc. An "incremental" backup is the differences between "now" and the last backup run, which could be an incremental itself. So your first delta will be 5GB, the second 5GB, etc, etc.

The advantage to the former is that restores are potentially much faster -- you roll your full backup, then the differential taken immediately after your restore point. The downside is that you potentially require much more media depending on your deltas.

The advantage to the latter is that you require less media, and backups potentially run faster since you are backing up less data. The downside is that to restore to a point in time you have to restore your full, then each incremental, in order.

Regarding your rotations -- if all you need is two weeks on site, then your pattern is probably OK. However we always use a fuller rotation.

  • First Friday of the month: the monthly backup. Sent offsite for one (or two) years (depending on the customer).
  • Second through Fourth (or fifth) Friday: Week A through C (or D). These are sent offsite and come back a month later.
  • Sunday through Thursday: incremental or differential backup, depending on the customer requirements and capabilities. These live for two weeks and stay onsite.

Some customers also want occasional special backups which go offsite forever or until recalled. Usually I roll two copies of these since media can degrade.

Finally, one note of wisdom: it isn't a backup until you test it. Make time in your cycle to regularly test the restore of various parts of your backups on a regular basis. Not only will this validate your backups, but it will mean you know what to do when a restore comes along for real.

If you read nothing else, read "Backups Suck" by M.Janke here: http://www.standalone-sysadmin.com/blog/2009/02/backups-suck/

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We each have different systems and needs, so we are all likely to give different recommendations. Do as KPWINC suggests and do some reading up. Then when you do implement it make sure you do it in a way that can be readily modified should you later determine a different system would be better.

Having said that, here is my recommendation:

You are only backing up a small amount of data, so if it's practical to do so run full backup each day. Backups will fail from time to time, for many reasons. Having a full backup on each tape not only simplifies restores but improves your DR chances.

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