[Tig] removable storage disks

[Rick Balabuck]

On Thu, 19 Jul 2007, Jack James wrote:
 > Hi there,
 > I'm wondering what experiences people have had with removable storage
 > disks, i.e. firewire and usb disks, especially high-capacity ones, in
 > terms of their reliability when sending them across the world. I'm
 > absolutely fed up of the appalling unreliability of lacie drives (my
 > last estimates were that about 30% seem to fail within a year), and
 > was going to go with G-Disks instead, but I'm hearing from a
 > distributor that they've been having lots of returns of those lately.
 > Any other options out there?

I purchased a 600GB LaCie "RAID 0" drive which did fail, but a bit
past its warranty period.  I should have known better than to purchase
any RAID 0 product since such products are at least 2X (but probably
4X) more likely to fail than single drive units.  I took the broken
unit apart and it seemed to be reasonably well constructed.  One of
the hard drives failed to spin up so the failure could be blamed on
the hard drive rather than LaCie's "value add".

There is an old adage "You get what you pay for" and I think it
applies here.  The market is very price competitive so vendors like
LaCie purchase the absolute cheapest drives with the desired capacity.
There are only three large drive vendors in the world (Seagate,
Western Digital, and Fujitsu) so you can be sure that the hard drive
comes from one of these makers.  At the typical price point, it is
likely that the quality of the drives will be the same.

Bob
======================================

Bob's comment about you get what you pay for is very accurate here.

Drive performance is based on 3 factors.
1) speed of the interface (USB, FireWire, SATA, SCSII, SAS, FIBRE)
2) density that the drive can support (which is usually determined in  
a testing cycle before the drive is branded as supporting a  
particular capacity) the more errors detected the lower the capacity  
and cost. All drives are essentially the same, the difference is in  
the density of data (lower number of errors = higher density &  
capacity) that it can support and the higher the cost
3) electro mechanical construction of the drive hardware which means  
specifically
- bearings ( think of the jewel mechanism on fine watches)
- head mechanism (how fast the head can move from track to track)  
servo is better than voice coil
- error detection software (how sophisticated is the drive in dealing  
with the inevitable physical errors that exist on the drive at time  
of manufacture) and which may develop over time as the drive spins  
and things start to wear out

The drive industry evaluates this in terms of MTBF and duty cycle,  
basically both refer to how well made the drive is and how long you  
can expect it to run without problems. Needless to say the best  
drives go to the biggest purchaser and cost the most, better  
technology (ruby bearings and servo head mechanisms) cost more than  
voice coil based systems and run faster, for longer and have more  
sophisticated error detection hardware & software all of which costs  
more.
So SCUSI and FIBRE drives are going to be better and lots more  
expensive and should last longer. The basic problem is that even  
these drives fail, but keep in mind that drives designed for  
occasional use in a personal computer environment (SATA with USB or  
FW interfaces) are at the bottom of the heap and most likely to fail  
as they are designed with a duty cycle of < 25%).

Be warned that trying to find out more about this information is  
really a challenge and will require a lot of web searching.
check out this article for more information.
Failure Trends in a Large Disk Drive Population
by Eduardo Pinheiro, Wolf-Dietrich Weber and Luiz Andr´e Barroso
Google Inc


Rick Balabuck