Backup is one (if not the) most boring subjects in the whole of IT.

Here's why

  • It looks simple
  • It looks easy

If you are thinking this - then Backup/Restore have already got your IT system marked for a disaster.

Problem with backup

No-one likes doing Backup's for lots of reasons

  • Takes time
  • You need to be methodoical
  • Need to be organised
  • Easy - therefore "beneath me"
  • Simple - only an idiot can get this wrong :)

Ah - yet more reasons to be very worried.

Reality of Backup

If you mess up

  • Fired
  • Company goes bust
    • Re-Pay bills
    • Re-Order stuff
  • Lost time/CPU Hours

Types Of Backup

There are basically 2 types of Backup

  • Full
  • Incremental

As often in IT there are good and bad things with each

Before I look at the types of Backup - you should be aware that there are generally 3 areas where you can backup to

Backup Media

  • Tape
  • Disk
  • Software with Tape/Disk

In the movies - you may have seen old large tape drive - well they still exist - but now come in small Watch-Sized boxes. They are efficient - cheap - reliable.

Tape drives however do need maintenance - and occasionally go wrong.

You can also back up to Disk. This is the fastest, easiest to add to the system (tape drives can be driver specific - and troublesome). Disk drives however can fail - and adding RAID-5 to them adds more to your costs.

Software with Tape/Disk. As your Backup's get bigger - then the usefulness of Software defined backup increases. This extra functionalty however will cost you $$$$'s but save in your disk/tape spending.

medium good bad
Tape Cheap Slow
Tape Been used for long time Needs maintenance
Disk Fast Expensive
Disk Easy to add/Expand Raid 5 more $$$
Software Lessens the backup Costs $$$

Full Backup

This is the easiest way to do a backup

You have a Computer system

  • Full Backup
  • We are now OK ?


You can not back up a live system and expect it to be rebuilt - the system devices/files/logs/password files etc on many Operating systems would not be compied correctly.

A full backup would only be suitable for a Data Directory/Files. And then only when the system is not being used.

Incremental Backup

The word incremental means "added to" - so an Incremental backup would only backup files that were added/modified (A directory would record that a file has been deleted).

This system is good - because it reduces the size of the backup's (after the first "Full Backup") - but if you then have 100 Increametal backups - and then your system fails. You will have to do a full restore - followed by 100 "Adds". The chances of this working well - are not good.

If you did a Full backup on Sat - and then 5 days incremental - this would be a better solution.

Backup Frequency

Usually most organisations have a

  • Daily
  • Weekly
  • Monthly

Backup policy.

I do know however some places that use a 1 hour backup policy !!

1 Tape from the Daily "Pool" - gets added to the Weekly "Pool". Then At the end of the Month - 1 Tape from the Weekly "Pool" gets added to the Monthly Pool.

This mechanism is sometimes called GFS


GFS stands for

  • Grandfather
  • Father
  • Son

Backup Understood

The #1 issue with backup is this

  • Never Checked
  • Never Tested
  • How Long will this take ?
    • London 1997 Bombing
    • 2 Days you went broke

It may be working in Jan 2014.... but things are different in July 2015.... New directories/Disks - Has your backup been updated/Checked.

Even if the backup's are checked - have you really tried to restore ?

Hardware changes Spare Machines needed

Even if you have this - do you have time ?

  • Developers do not like this work*
  • Ops staff a best for this

Keep the tapes where ?

The Tapes (obviously you can not move the disks) should be kept in adifferent location.

So Machines in 1 Building - tapes should be in another.