Number 244 - September 2003

Blessed Are The Pessimists For They Hath Made Backups
by Tom Coleman - Reprinted from June 2003 PC Update, Melbourne PC User Group, Australia Our inimitable Tom Coleman reviews old methods and problems and introduces us to some new concepts in the field of Data Integrity
Let me state right at the start that this is not instructions on how to make a backup. This is a discussion on the current state of the art and consideration of some of the options.    Once upon a time you needed almost sixty floppy disks (that's 360k DSDD 5 1/4 inch floppies) to back up your 20 MB hard disk. Well of course things changed and the floppies became 1.2 MB and there was rejoicing in the ranks because now they could feel less guilty because it now only required about 17 floppies. And then the advent of the high density 3.5 inch floppy reduced it to 14 floppies. Let's Take A Side Track    Information on all drives is stored on sectors. A sector is a short (string) clump of magnetic impulses that holds 512 bytes of information. (Regular readers will know how I love to lie to them. There are in fact a few more bytes at each end of the sector for housekeeping but they do not contribute to storage capacity) Now the mathematically astute will know that 512 bytes is half a kilobyte. For the mathematically numb a kilobyte is 1024 bytes (or, if you like, two sectors).    Well that is true in the real world, but such truths are to be tweaked and fiddled with in the LaLa land of computer salesmen. Let me give you an example.    The standard 3+ inch HD floppy disk has 18 sectors per track. A track being a circle of sectors on the disk. There are 80 tracks on each side of the disk. So this means that there are 2 times 80 times 18 sectors on each floppy. Come on now, out with the calculator and check me. That's 1440 Kilobytes or if you like 1.44 thousands of kilobytes. Because there are 1024 KB in 1 MB (one megabyte), this means that the disk holds 1.4 MB (Oh all right! 1.40625 MB) What a pathetic way to make a disk seem bigger. Why did they not decimalise the kilobyte too. That way they could have had a 1.47456 MB floppy. It sounds bigger. The most likely reason is that computer salesmen don't know much about computers. It gets worse.    Your "Mine's bigger than yours" hard disk sales force advertises hard disks in millions or billions of bytes. So the 40 GB hard drive you just bought comes up as a 37.25290298 GB drive when it is installed into your computer.    Have you been robbed of two and three-quarter gigabytes?. No you haven't but they hate people like me pointing out the difference between a decimal gigabyte and a binary gigabyte. It makes them look petty and silly. Time To Get Back On Track Again    So it turns out that you could fit all of your 20 (decimal) MB hard disk onto just fourteen 3+ inch floppies. Such a small task to save your bacon and your files and your soul from eternal damnation and the tut-tutting head shaking that goes on at hard disk wakes.    Guess what? Hardly anyone backed up. It was so easy, but none but the paranoid did it. "Blessed are the Pessimists..."    So where does this put us now. A 20 GB hard drive is a thousand times bigger than a 20 MB drive. That cuts out floppies for two reasons. First 14,000 floppy disks is just ridiculous and second at 25c each for bulk buying it would cost $3,500 and take just short of 10 days, non stop, allowing a minute each. Longer if you have a slow floppy drive.	Of course the tape drive people have come a long way and tape speeds are now much faster than they used to be, but there are problems. They still take hours. It is frequently difficult to recover a single file.    Not just tapes but all forms of backup fail when they fail to restore. You may not know that you have a crook backup until the restore bombs. Typically that's when it is too late to fix. This applies to floppy backups too. But the reason that most backups fail is that people don't do them.    It's the same now as it was when 14 floppies were enough and it took 15 minutes, or half an hour if you had a slow drive.    George Skarbek made me famous for saying "Backups are done tomorrow. Hard disks go down today".    Nothing has changed. To get a good backup system we need to remove operator. The fact that people were involved and they had options such as, later, meant that it was just never going to get done. That is the fundamental problem with all backup systems. Someone has to do it.    God moves in mysterious ways. The truth has been around for many years. It might have been a bit expensive at one time, but is now coming and is affordable.    RAID is a series of protocols covering things to do with multiple hard disk drive arrays. The various functions are called RAID 0 or RAID 1 and so on. Go off and read up on RAID arrays if you want to know more. We are interested in RAID 1. This covers disk mirroring. Once it is installed with two drives the second drive continuously makes itself as a copy, a duplicate, of the first. A permanent back up. The protocol provides for impeccable copy verification.    If RAID 1 is fully implemented, should the first drive fail then the second just takes over, seamlessly. If the second drive was a removable drive and you were a bit slow about putting it back at the days start, you needn't worry as it will update itself in the background once you get around to installing it.    So how do you install RAID 1. It is a hardware/software installation. These days you can buy motherboards with RAID 0 and 1 built in. Sometimes maybe 3 and 5 as well. There are a couple of sockets on the motherboard, like IDE fittings, and you attach your drive cables to them. You will need to purchase a second hard drive. It does not need to be identical but needs to have adequate speed and capacity.    If you are not buying a motherboard then you need to buy a RAID card. It is a PCI card and benefits from faster PCI and FSB (Front Side BUS). Once you have installed the card and the hard drive(s) there is a simple software installation and you are up and running. Take a copy of your hard drive home with you at the end of the day if you like.    You do not have to do anything. It works with or without you. It works in spite of you.    Operator resistant backup. It is the future. You read it first in PC Update!
Number 244 - September 2003