Date   : Thu, 12 Nov 2009 01:52:18 +0100
From   : rick@... (Rick Murray)
Subject: Help! [ot]

Anders Carlsson wrote:

> image every 5 seconds, basically writing to the same block all the
> time. After a year or so, we encountered unrecoverable R/W errors
> on that HDD,

Strange - SMART and the like should have swapped out bad sectors...

...though, perhapsthis should serve as a warning, keep a rotation of 
files periodically 'tidied' even if old files are no use whatsoever, at 
least the data will be spread around.


> On the other hand if we had stored 24 hours worth of webcam images
> the problem would never have arisen and the machine could probably
> have been running for 30 years before the HDD broke down due to a
> sector written too many times.

Or the drive was faulty, or the interface was faulty, or you had a minor 
earthquake/powercut/etc...?


> The topic of write cycles on memory cards obviously has some relevance

I am led to believe that decent memory cards manage the memory in such a 
  way as to ensure no one sector is ever overly abused ("load 
balancing"), bearing in mind a Flash "sector" could be in the order of 
128K. Certainly I believe this is why a device with a rated rewrite 
capability of a hundred thousand writes is considered acceptable for use 
as a computer SSD. Balance the load around, before the part physically 
wears out it should offer a service life not unlike that of a 
traditional harddisc.


> However even at 10,000 write cycles one would be hard pressed to wear
> out a SD card or alike, and those can be replaced after 5,000 writes. :)

But the question is - if you write and rewrite the same thing, is the 
load balanced or not on an SD card? Is a sub-tenner SD reliable to that 
degree, or is it just a disc controller faker plugged into a wodge of 
flash and your X-thousand cycles is all you get?


BTW: Remember on NTFS that the system keeps three dates: Created, 
modified, last accessed. This means metadata is WRITTEN just for reading 
the file.
Didn't Acorn's early DFS have a cycle count in the catalogue that 
incremented each time the drive was accessed?


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
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