Verifying data

[Steven4567]

I recently started using a external hard drive (Seagate 1TB expansion HDD) that I have rarely used over the last 3 years (Used more or less once every 6 months to add (around 20GB) of files and only 8 and 3 months ago to copy (200GB)

I've realized that the hard drive contains files that are only present on said HDD, I've copied the files off to another computer.

I'm curious if there is a way to verify all the data has actually stayed over the last 3 years or if some have been lost, I'm not entirely sure how Hard Drives operate so what worries me if the drive has lost some data to it losing its magnetic field, cable was damaged (not sure how to test the cable), it corrupt when copying, or some other fault could have occurred. 

I have ran the seatool tests: Short DST, Short Generic, Smart, Identify, and Long Generic, they all passed. I've also ran Chkdsk with the option "Scan and recover bad sectors" it also ran successfully, I've also ran Dells support assist application with both its long and short tests, they both passed. Crystal Disk Info also says the drive is healthy. 

I'm not sure if all this was overkill, but it has data that is really important to me on the drive, my question is, do all those tests passing show the data is all correct, fine, present and uncorrupt? Or what other tests do you recommended to make sure its all there and doesn't need sending to a recovery firm.

 

Thanks in advance

[Steven4567]

Got this really in depth and detailed response from asking GoodBytes in a Message, posting it here in case anyone in the future has the same question as I did;

1 hour ago, GoodBytes said:

Hey!

 

HDD's retain data for many years. The mechanical part will definitely break from not being used for very many many years before the data disappears (mostly due to lack of lubrication of the motors and head movement), and even then. I still have my old 120GB from 2001 drive, and I have no problem reading any of its data last I tried... 2 months ago. That has been about 12-13 years last used before that, totally unplugged.

 

The only issue HDD is sensitive is being close to strong magnets, or static shock breaking the circuitry of the drive, or physical damage, including too much pressure applied on a laptop HDD top cover bending the metal cover blocking the mechanical system from working.

 

Drive health doesn't tell you if you have data loss. Data loss cannot be detected. The best things that will point you to data loss, is if the data got corrupted. Drive health will only tell you about bad sectors or incorrect drive operation. Bad sectors are sectors in the drive where the drive failed to write successfully, where it got something blocking the head (dust or even smoke particle), or metal plate is faulty and can no longer be magnetized.

 

The way a HDD/SSD works is like so:

When you put a file on the drive, the drive write it, and it adds the file in its journal. The journal is a directory of address. See it as a phone book. This keeps track of all files, if the file is not in the journal, the file is considered that it no longer exists, even if it is still there on the drive. In fact, when you delete a file on your system, it only deletes the entry in the journal, it doesn't actually set the bit to 0 where the file are. This is done to accelerate the process as HDDs are super slow. It does many cut corner tricks, if you wonder.

 

So if you have a file corrupted, you'll see in the journal that the file is there, but when you try to read it, the program opening the file, is unable to as it unable to read it properly. If it where a text file (.txt), you would see in Notepad that the file starts fine, and then the text becomes random symbols and whatnot.

 

The chances that a corruption happens on the journal where only 1 or 2 files are gone and not the rest, is extremely rare. You have to be very unlucky for this to happen. Either everything or almost is gone, or the journal is not affected and a or some or many files are corrupted.

 

Hope this helps!

 

 

[Mira Yurizaki]

The way people usually verify the integrity of the files is to run an MD5 hash on it (or some other kind of hash). But this requires some forethought beforehand. Otherwise, if you had the hashes of your files, it would be easy enough to create some sort of program or script that crunches the hash of the file currently vs. the computed hash. Of course, if you changed the file, you also need to update the hash.

 

Otherwise, you're going to have to verify each one manually if you have no other catalog of such.