Theoretical and practical about hard drive storage

[kenny1999]

Hi

I've done extensive research on web about hard drive and storage. There are something I feel quite surprised after having used computer for more than a decade.

It is said that a file stored on a hard drive, even not being played, used or edited could lead to big (or tiny) corruption over time. (scientifically mean their checksums changed)

It is said that if the USB cable of an external harddrive was not safely removed or if the power is shut down correctly, it *could lead to damage to the hardware, lead to bad sector and thus - data corruption might occur.

Now my question is, I understand all these theories.

But I would like to know how likely could these happen

1. Unused and unedited data corruption over time (within 3 year)
2. Abnormal unplug of usb cable (without safely remove), or power shut down abnormally

Is it really that easy to happen? (if I hope the MD5 or other checksum of a random file (assume no intentional edit of course) will not change within 5 years, is it easy or difficult?

My situation - I've got quite a number of files that I don't want their MD5 (or other checksums)to be changed and stored them for years. However, I've unplugged the usb cable for some time without safely remove and there were some sudden power cut / instability occasions happening.

I don't know if those few power cut and occasion and "unsafely" remove are likely to lead to the checksums of the files changed (they were inactive and were not transferring or copying etc when those instances happened)

THanks you every body

 

[Aastii]

1. Hard drives work my magnetising sectors of the platter. Magnetised = 1, not =0, there you get your binary and stored data. All feromagnets, which the surface of the hard drive is, are not permanent unlike the name "permanent magnet" would suggest. Over time they will lose their field strength, and so sectors that were magnetised will become de-magnetised.

The exact rate at which this will happen, I couldn't say and to be honest, I am not sure anyone can for certain, but if you were that worried, you can periodically copy the data to another location and then copy it back, refreshing the magnetisation.

2. Generally damage will only occur if you are currently transferring data, as you will stop part way through a write process, only having part of the data and as the data is not contiguous, you will unlikely be able to pick up where you left off.

For your situation, nobody can say for certain if the data will remain intact after 5 years, but I do not see a reason that it will not, 5 years is not a huge amount of time after all.

For your disconnections, why not just check the files that they are still all working fine? Without writing to those sectors when you disconnected it is extremely unlikely that there is any damage to the data

 

[kenny1999]

1. Hard drives work my magnetising sectors of the platter. Magnetised = 1, not =0, there you get your binary and stored data. All feromagnets, which the surface of the hard drive is, are not permanent unlike the name "permanent magnet" would suggest. Over time they will lose their field strength, and so sectors that were magnetised will become de-magnetised.

The exact rate at which this will happen, I couldn't say and to be honest, I am not sure anyone can for certain, but if you were that worried, you can periodically copy the data to another location and then copy it back, refreshing the magnetisation.

2. Generally damage will only occur if you are currently transferring data, as you will stop part way through a write process, only having part of the data and as the data is not contiguous, you will unlikely be able to pick up where you left off.

For your situation, nobody can say for certain if the data will remain intact after 5 years, but I do not see a reason that it will not, 5 years is not a huge amount of time after all.

For your disconnections, why not just check the files that they are still all working fine? Without writing to those sectors when you disconnected it is extremely unlikely that there is any damage to the data

Hi, some files could still play correctly and could not be noticed if they are changed/corrupted very slightly. Especially video files and picture files. Executing a file cannot test if they are intact and perfect. You might wonder then why I care about the checksum of video files / picture files. Sorry but this is a personal reason that takes time to explain.

Or I should ask my question in this way, while those ''theories'' exists (like unplugging usb cable without safely remove, powering off the device suddenly, or slightly move the harddisk during operation, could lead to slight hardware damage), I would like to know if the technology of hard drive nowadays are that vulnerable

I can understand, by common sense, *during* copying before 100% , sudden unplugging would be very likely to lead to data corruption, it does make sense because the data is transferred by the cable, it does make sense!

but i don't know if those thing which doesn't make sense to me could happen easily as well.

Thanks