Availability Tools

Data loss causes, according to Ontrack engineers (who seem to have lost no data to malicious intruders):

According to a Gallup poll, most businesses value 100 megabytes of data at US$ 1,000,000.

Disk Longevity and Failure Rates

Summary: All media erodes, ink on paper is far better than any magnetic media, and we just don't have enough information to really say how long optical media is likely to last. The longevity of the logical format may be more important. Consider that the last heiroglyphs were carved in 394 AD, but soon after that we lost the ability to read the still very sharp and distinct writing. Also consider that the Dead Sea Scrolls are ink-on-parchment technology about 1900 years old but still readable. Egyptian papyrus is up to twice as old also also readable. The oldest true paper we have is from 868 AD. But computer media from a decade ago is often useless.

How long do you expect a disk to last before it fails? Is one brand better than another?

Disk manufacturers do studies, but they are accelerated failure tests on their own systems only under very specific conditions. Any manufacturer can have a short run of worse or better devices, and comparisons between various manufacturers' products haven't been very meaningful.

Their study was based on over 100,000 disk drives, a variety of PATA and SATA from a variety of manufacturers, 80-400 GB and 5400-7400 RPM. They do not provide information about the specific manufacturers, but that really isn't all that important. All manufacturers have short runs of worse and better quality, and an attempt to measure who was better would probably be overwhelmed by measurement noise.

Some SMART parameters are highly correlated with disk failures. However, SMART parameters alone are not all that useful for predicting individual drive failures.

Contrary to common assumptions, temperature and activity are not highly correlated to drive failure.

Drive manufacturers quote yearly failure rates below 2%, but user studies report up to 6%. Many apparent failures in the field don't seem to be failures in the lab — maybe the problem was with a specific controller or data cable. They cite other studies of failure rates:

Study of 368 SCSI disks over 18 months, 1.9% failure rate.
Study of 2489 disks at archive.org over 12 months, 2% failure rate (although up to 6% per year in the past).
Study of 15,805 and 22,400 disks at each of two large web hosting companies, 3.3-6% failure rates.

Some SMART data is clearly bogus. I agree — one of my disks seems to consistently report its temperature in degrees Farenheit instead of the expected Celsius, and so it appears to always be somewhere above the boiling temperature of water.

A significant number of drives fail within the first 3 months. The weak ones die quickly.... Then the failure rate climbs after two years. Annualized failure rates, approximated from their Figure 2:

0-3	4-6	7-12	13-24	25-35	36-48	49-60
2.8%	1.7%	1.7%	8.1%	8.6%	6.0%	7.8%

Four SMART parameters were significantly correlated with increased failure rates.

Error type	Meaning	After the first such occurance of this error, this many times more likely to fail within 60 days than a drive without this error
Scan error	Drives typically scan the disk surface in the background and report errors as they are found. Large scan error counts may indicate surface defects.	39 times more likely to fail
Reallocation counts	Drive's logic has remapped a faulty sector number ot a new physical sector drawn from its pool of spares, because of recurring soft errors or a hard error. May indicate drive surface wear.	14 times more likely to fail
Offline reallocation	Subset of the reallocation counts, counting only reallocated sectors found during background analysis. Should exclude sectors reallocated due to errors during actual I/O.	21 times more likely to fail
Probational counts	Suspect bad sectors put "on probation". Weaker indication of possible problems.	16 times more likely to fail

But while that looks impressive, over 56% of the failed drives had zero counts in all four of those SMART parameters! So, models based only on those four signals will predict less than half the failed drives.

Archiving

Laptop Theft Prevention

Spam, or Unwanted Junk E-Mail

How can you tell where spam was injected? Read the "Received:" fields in reverse, looking for inconsistency where the promiscuous relayer accepted the spam from the source. Using a real example I received, my comments inserted below the relevant lines in red:

Further investigation could use traceroute or whois to figure out where 216.77.220.220 really is in case the reverse resolution above either failed or was faked. As per the GNU version of whois

Hardware or Systems Malfunction	59%
Human Error	28%
Software Program Malfunction	9%
Viruses	4%
Natural Disaster	2%

Estimated longevity of electronic storage media, in years
CR-R (cyanine & azo dyes)	7
CR-RW, DVD-RW, DVD+RW	7
Flash RAM	10
Digital tape	13
Analogue tape	20
Audio CD, DVD movie, CD-R (phthalocyanine dye and silver metal layer), DVD-R, DVD+R	25
CD-R (phthalocyanine dye and gold metal layer)	100
From "Now we know it...", New Scientist, 30 Jan 2010, pp 37-39.

Availability Tools

Data Loss Costs

Disk Longevity and Failure Rates

Archiving

Laptop Theft Prevention

Spam, or Unwanted Junk E-Mail