The drive reliability ratings on these pages are based on our own experience with the particular drive model. Nothing else.

If you want to know which drives are the most reliable, there is simply no substitute for having a good number of the model out in service. For these pages we consider our actual service failure rates and only our actual service failure rates.


Explicit Ratings
AAAOutstanding, one of the most reliable drives we have ever seen. No new model ever gets this rating, we have to gain enough experience with them first. Very few drives get the Red Hill AAA rating.
AA1Excellent: as good as or better than most drives on the market. Some of our AA1 rated drives have a 100% reliability record — but we only give a AAA rating when we have seen large numbers in service for a good long while.
AA2Very good without being outstanding. Typical of most good quality drives on the market. You can still feel quite comfortable with an AA2 drive.
AA3Can still be worth choosing these, but be aware that they fail more often than the higher-rated drives.
BABelow average. Not generally a good choice. Ranges from somewhat below par to the truly dreadful. See the text for details.
Uncertain Ratings
No DataOur reliability ratings are based on our own experience in the workshop. We do not assign any reliability rating to drives unless we have met enough of them, and had them in service for long enough to feel confident of our opinion.
AAXWhile we don't yet have enough experience with these drives to assign them a proper rating, early indications are good. If we see enough of them for long enough, we will be more precise. Notice that low-volume drives can stay "no data" or "AAX" for a long time, sometimes forever.
AAYAnother category for drives we have a modest amount of experience with: enough to feel a little uneasy about them, but not enough to justify a proper numeric rating. While our observed failure rate for these drives has been higher than average, this may be simply chance. We need to see more of them to be confident.
WARNING Reliability ratings reflect our own knowledge and experience. They may be unfairly complimentary or critical in cases where we have simply had very good or very bad luck. No drive can ever be regarded as 100% reliable—not even an AAA-rated model. Hard drives are electro-mechanical devices and any such device can fail—with or without warning. Nothing can substitute for proper backup of your data. If you don't already have good backup for your system, call us for help. It need not be expensive. Remember the four causes of data loss


Of course, it's never possible to be 100% sure of the reliability of a drive until it's obsolete. We can estimate the working life of, say, an ST-225 very well, because they came out in 1984 and we have seen hundreds of them over the years. And, yes, a few people were still running them up until quite recently!

Notice that it is easier to assign a poor rating (AA3 or BA) than a good one. If a drive has a very high failure rate, it becomes apparent even with a small sample, but a low or moderate failure rate can only show up with larger numbers.

Also take note that reliability standards change over the years. Do not make the mistake of thinking that because the 1984 vintage ST-225 and the 2001 vintage WD Caviar 400BB are both AA1-rated drives that you could expect to see the same failure rate per thousand shipped! The ST-225 and the 400BB are, however, similar in that both have shown themselves to have low failure rates by the standards of the day. Modern drives give far less trouble than older ones used to, and put up with far worse abuse before they fail. There is not a drive on the market today that would not rate an 'AAA' by 1984 standards, or indeed by the standards of 1994

We don't even try to assess a reliability rating for SCSI drives. We don't see enough to have a fair sample size, and as you would expect from drives that typically cost betwen three and eight times as much as their more humble mass-market siblings, they are probably all in the 'AAA' class in any case.

Data loss in perspective

For all our emphasis on hard drive reliability, actual hardware failure is in fact a rather rare way to loose your data. Even the poorest drives are vastly more reliable than the human beings who operate them. If you have never lost important data through your own stupidity, then you have probably never used a computer, or perhaps just never used one for anything that matters.

The table below lists the main causes of data loss in order of frequency.

The Four Causes of Data Loss
User Error

Otherwise known as "Woops!" This is easily the most common cause of lost data. There are many, many ways to do this, ranging from dropping a file on the shredder when you meant to drop it on the printer, to the classic DOS combination:
C:\> DIR A:     (nothing important)
C:\> DEL *.*   ('oh %#@^$#!')

Malicious Damage

Most people are reasonably virus-aware — though none of us are as careful as we should be. Most virus problems can be cured with little data loss, provided they are attended to promptly. Having sensible email handling procedures and a decent anti-virus software package is sufficient protection for most people. But if your anti-virus software is not up to date, it is quite useless! And if you are still using Microsoft Outbreak, er Outlook as your email client after the Love Bug and Melissa and all those countless others, then you deserve what you get. We have no sympathy at all for Outlook victims. Ditto for people who get massive spyware infections because they insist on using Internet Explorer instead of any of the modern browsers (Mozilla, Opera, Firefox).

Software Error

While hardware gets more and more reliable every year, software only seems to get worse. (Actually, it's probably much the same as it was 20 years ago—it just seems worse.) Badly-written games cause quite a lot of damage to our fragile file-systems. Over-ambitious utility programs that claim to give you something for nothing are another common problem. (Double Space was one, but there have been many others.) And even "safe" office productivity software has its failures. Believe it or not, we still get calls from users who are about to loose a whole document because of the infamous "can't save" bug in Word for Windows.)

Hardware Failure

The least common of the big four, but still a possibility you can never afford to ignore. Hard drive failure can happen without warning, and at any time in the life of the drive. The best drives fail less often, and may even fail gracefully so that you get some warning and can look to your backups, but they still fail. There is only one real rule of data safety: backup often! Since the advent of the CD burner, there has been no excuse for not backing up.