Backups

In a perfect world, nobody would make mistakes, disaster would never strike, and backups would not be necessary.

In real life, however, computers do sometimes crash or get infected with malware, to name only a few of many threats your data is exposed to.

We all know, of course, that we should make regular backups to prevent the loss of data turning into a disaster.
Well, in fact, just making backups does not suffice, verifying the restore procedure is equally important!

I recently read a report stating one third of small businesses do not make backups at all.
Though my own guess would have been worse, it still is a shocking number, considering another report stated that 90% of businesses don't survive a major data loss.

The number of private computer owners not making backups are, most likely, far worse.
Though the financial impact for private computer owners won't be as dramatic, it really does hurt to lose one's family photo album.

So, look at backups as an investment.
It is like a health insurance policy: consider yourself lucky if in the end you have invested "for nothing".

If we agree on that, the next question is how much (time and money) you are willing to invest.
It isn't realistic to try and prevent every type of mistake or failure, but it is possible to get close.

Apart from clustering, the best option would be multiple full backups (plus at least one image backup for disaster recovery) every day, written on read-only media, and a duplicate stored off-site:

• full backups require less search time when restoring individual files
• image backups save the day when a disk or server fails
• read-only media prevent corruption of existing backup sets by malware (e.g. ransomware)
• duplicate backup sets stored off-site allow restoring your data even after a malware infection, fire, flood or earth-quake

The table below lists some of the techniques used to protect and backup your data, and what they can and can't do.

I included several techniques that can improve the availability of your data, like RAID, clustering and version control, but using these techniques does not mean you can forget about true backups!

It is better not to rely on a single backup technique, but to combine several techniques.

For your servers, you'll need at least some disaster recovery techniques (to restore a crashed server from scratch, on new hardware, fast): maybe a combination of mirroring, clustering and image backups of the boot partitions.

For the data on the servers you'll need full backups on rotating media sets, either daily (or even multiple backups daily) or weekly plus daily incremental/differential backups.
A media rotation schedule that is often used is daily incrementals (or differentials if you don't mind the larger backup size), rotated bi-weekly, weekly full backups rotated bi-monthly, and monthly backups rotated per year.
An alternative option found in some enterprise backup systems is to keep only a fixed number of file versions. In practice, I have always found it hard to explain to customers why I could restore their reports from 3 years ago, but not their e-mail from 3 weeks ago.

You probably need to archive some data as well, which requires non-rotating media sets.
Keep in mind that you'll need to test and/or rebackup (restore and backup again) archived data on a regular basis and with every upgrade of your backup software or replacement of your hardware (tapestreamers etc.), as no backup medium nor backup file format will live forever.
Backups on CD/DVD may be easy to restore on other hardware, but the expected 30 years lifetime for (pressed) music CDs does not apply to (recorded) CDR/DVD±Rs (3 years is a more realistic figure).

A final sidenote: even if you can restore your files, you still need the right software to access restored data, e.g. I still need to keep a copy of the WordPerfect installation disks (and the serial numbers) to make sure I can read my old documents.