[clug] Recovering data from old disks. Max age observed?
George at Clug
Clug at goproject.info
Fri Jun 14 10:49:09 UTC 2019
On Friday, 14-06-2019 at 16:37 steve jenkin via linux wrote:
> I recently read the contents of a 2010 x 1TB USB-2 external hard-drive that had Apple “Time Machine” data on it.
2010? Why that is just recent times. In the last few weeks I have been attempting to turn 1.44mb floppy disks into *.img files for use with virtual machines.
MS C++ 1.0, Disk 3 of 20 had errors, the rest were fine. As yet, I have not tried to install from the collected img files, so I have not learned whether the errors on disk 3 will be an issue or not.
I think I read somewhere that hard disk drives continually refresh data on the drive by reading and writing data back again, so if the drives are not powered on, the magnetism slowly fades, loosing data. That said, I have had success with drives much older that 2010.
I also have an archive of 51/4" floppies, I guess by now they will be blank disks, even if the glue binding the magnetic material hasn't decayed by now.
With Hi8 video I filmed between 15 to 27 years ago, I was surprised to find that some cheap tapes retained data where as the higher quality tapes I had purchased in the hope of a longer file span, had degraded.
I have tried CD and DVD storage but plastic degrades, DVD and BluRay ink fades.
I think the only way to keep data living it maintain multiple copies on running systems. I guess (bit) data errors would still creep in over time and eventually be an issue.
I wonder if in 4,000 years what records of our time will still exist, and how will recorded history at that time will explain the emergence of the digital age, early computing systems (particularly our early CPUs) and the "personal computer".
The span of recorded history is roughly 5,000 years, beginning with Sumerian Cuneiform script; the oldest discovered form of coherent writing from the protoliterate period around the 30th century BC.
Two issues ago, I reported that when a hard disk is powered down and stored on the shelf, after time the magnetic data will tend to slowly “evaporate.” (Here’s the original article.)
The basic problem is that magnetic data stored on the drive fades, or loses it charge, over time causing you to lose all the data on that hard disk. (I’ve been told the term for this data loss is “bit flux.”) This data can start to disappear as early as a year after the hard disk is powered off.
... All hard drives are programmed to refresh data as the heads skim along the drive. But that only happens when the hard drive is powered up and operational — something not possible when it is sitting on a shelf.
How often you should perform this exercising of a hard drive is difficult to say, but once a year or once every two years would be a good starting point.
> Had to resort to ‘ddrescue’ - there were 17 hard errors detected.
> The important points here:
> - old disk had been sitting collecting dust for years. Perhaps out of service in 2014.
> - I not pressing it back into service, just hoping it’d hold together.
> Now I’ve got the data off, I can discard the hardware.
> Newer disks are higher density, meaning finer tolerances, more complex engineering (surface lubricants mandatory now) and possibly more susceptible to data loss because the sub-systems are closer to theoretical limits.
> I don’t expect to be able to recover data from my 2015 disk in 2025.
> But how can ‘ultimate life’ be calculated?
> Other people much have recovered data from old disks, even used disks continuously (daily or weekly), for much longer than the nominal design life of 5 years.
> The contra for long lived drives is all the drives that fail early… The random factors combine to shorten and extend life.
> I’ve come to realise I now have to consciously ‘curate’ my old data if I want to keep it.
> Which means saving filesystem image [or LVM],, not direct to partition, ‘data scrubbing’ often enough to be happy with finding latent errors, and an intentional “collect, copy, retire” activity.
> Haven’t got there yet, only just starting. Still haven’t even found / collected all my old disk drives :)
> Steve Jenkin, IT Systems and Design
> 0412 786 915 (+61 412 786 915)
> PO Box 38, Kippax ACT 2615, AUSTRALIA
> mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin
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