How long can we keep data intact? Surely a very long time..? Not necessarily! A few events over the past few months got me thinking and it turns out that keeping data over long periods of time is pretty challenging. Let's see why.
What's Data and How it's Stored
Data is technically not something physical. It is a representation. Consider CDs/DVDs for instance. What is the physical difference between a blank disc and a written disc? It's that the reflective surface is no longer as reflective as it used to be! This is because a pattern has been etched over it representing the data. The surface itself is not technically data but the pattern it represents is. As long as the pattern lasts and remains accessible, data will be intact. Damage or distortion of the pattern means a change in the sequence of data. And like all things, the physical representation is subjected to change with time.
For the common optical storage(CDs, DVDs, Blu-ray, etc.), this means prolonged exposure to sunlight or a scratch on the reflective surface can alter its data. And it's not something uncommon.
Data in HDD and SSD Storage
Consumer hard drives implement 2 different technologies commonly to date: magnetic hard drives and solid state hard drives. In magnetic hard drives, data is represented as patterns of magnetic fields on rotating disks whereas solid state drives store electrical charges. In contrast to the optical storage, they perform better in regular frequent usage.
Disk Rot and Hard drives
The commoner hard drive is magnetic. Data is encoded in a series of tiny magnetic fields on a surface. Naturally, the strength of the magnetism decays with time. It is particularly significant when bits of data are stored closer and closer to each other in attempt to squeeze more data in a smaller space. Opposing magnetic fields closer to each other interacts, promoting decay.
This phenomenon is named 'disk-rot' or 'data-rot' or 'bit-rot'; the loss of data on a disk over time even when not used.
It used to be relatively common in the early days of data storage, particularly with magnetic tapes. To avoid loss by data rot, data had to be rewritten from time to time keeping the patterns fresh.
While modern magnetic hard drives do not share the same fate under normal circumstances, it does not mean it's immune to the test of time. Most people upgrade their computers within a few years of use. Thereby old data is freshly written on to a new disk. This is a time frame too small for disk rot to set in.
A Story
I happened to deal with a windows PC which has been in regular use for over the past 10 years. It had been working flawlessly until a few months ago before starting to lag now and then. It got worse over time, making the PC pause for longer and more frequently and then getting stuck for no apparent reason.
It seemed that CPU, RAM usage and disk activity were within range, no recent changes had been made and no obvious hardware or driver issues.
It seemed that CPU, RAM usage and disk activity were within range, no recent changes had been made and no obvious hardware or driver issues.
Antivirus and malware scans were negative and the windows check disk utility (chkdsk) did not return errors or bad sectors. But something kept telling me not to trust the hard drive. I backed up the data and did some reading.
It seemed that disk rot could be the culprit here.
The operating system was installed 10+ years ago. Microsoft Windows does not re-write aged data blocks automatically. So, most system files (and their magnetic patterns) on the hard disk may well have undergone physical decay. My guess was that when the hard drive tries to read those data blocks, it may be having a difficult time picking up the magnetism. It might be the cause for the lags and pauses.
The best option would be to reinstall the operating system afresh and follow up with the drivers and applications. But since I was keen on seeing if this actually was disk rot, I decided to restore the magnetic strength of the stored data by a re-writing process.
Utilities
It turns out while there are tools and utilities for this, most are Linux based. On the other hand, the few tools for Windows were pretty dated with the risk of having compatibility issues.
I decided to use DiskFresh(for link see below) tool. It's not a bootable isolated environment. So I was a bit skeptical because in this case, re-writing system data is critical. Somehow, it claims to runs alongside windows and still manage the full disk without clashing with the operating system. DiskFresh took a few hours to complete. To be honest it wasn't the smoothest experience. Knowing that all data is at the mercy of a re-writing app was not all that easy!
I decided to use DiskFresh(for link see below) tool. It's not a bootable isolated environment. So I was a bit skeptical because in this case, re-writing system data is critical. Somehow, it claims to runs alongside windows and still manage the full disk without clashing with the operating system. DiskFresh took a few hours to complete. To be honest it wasn't the smoothest experience. Knowing that all data is at the mercy of a re-writing app was not all that easy!
The lagging was gone after a reboot. It worked! The computer seemed faster and responsive.
Conclusion
Disk rot is not a thing of the past. We just have managed to slow it down to a point that we may have moved past by the time disk rot sets in.
In fact, the growing popularity of SSD hard drives might cause a resurge in the phenomenon. Solid State Hard drives store data as electrical charges. Electrical charges decay much faster than magnetism! SSDs mitigate decay by restoring the charges from a power source whenever possible. While it can be done very very quickly, leaving a SSD unplugged poses a real risk of data loss via discharging. As of the moment, time till disk rot in consumer SSDs ranges from months to around a year or so.
In fact, the growing popularity of SSD hard drives might cause a resurge in the phenomenon. Solid State Hard drives store data as electrical charges. Electrical charges decay much faster than magnetism! SSDs mitigate decay by restoring the charges from a power source whenever possible. While it can be done very very quickly, leaving a SSD unplugged poses a real risk of data loss via discharging. As of the moment, time till disk rot in consumer SSDs ranges from months to around a year or so.
Links / More Reading
https://en.wikipedia.org/wiki/Data_degradationhttps://superuser.com/questions/284427/how-much-time-until-an-unused-hard-drive-loses-its-data
http://www.puransoftware.com/DiskFresh.html
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