Is 1TB = 1TB? Need drive EXACTLY the same size.

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Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Sun Jul 01, 2012 6:01 pm

Does anyone know if all, or even most, 1TB hard drives are the same size?

I need to clone an old (first version) 1TB Caviar Black drive so I can try to recover an overwritten header. I don't want to write anything to the drive I have, so I will clone it and attempt to restore the header on the cloned drive. The embedded backup header is a known offset from the end of the physical drive, so I believe I need the drive I buy to be EXACTLY the same size (can't be 1 byte difference). I assume if I buy the exact same model drive I will be ok. But what about the newer 64MB cache version of the 1TB Caviar Black? And what about a Seagate 1TB drive? Is there a resource that can tell me the exact size of a hard drive before I purchase it? Any insight would be appreciated.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Sun Jul 01, 2012 6:23 pm

Unfortunately the only way to be sure you get the *exact* same size is to get the exact same drive from the exact same generation. Even models in the same family have slightly different sizes as gb per sq.in. increases.

Could you get it done with a slightly different drive that's slightly (or even much) bigger? Could you get, say, a 1.5 or 2TB drive and do your cloning? I mean, once you know the exact offset on the repalcement drive is there a way to write to a different block?
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Sun Jul 01, 2012 10:24 pm

Thanks for the input!

I don't think it'd be possible to use a different size drive for my needs, as it was a truecrypt encrypted drive, and the only way truecrypt knows where the backup header is located is by counting the byte offset (it appears as random data until it inputs the password you enter). As you suggested I probably could use a hex editor to manually copy and paste the end header, but I don't know if changing the number of sectors in between the header would have an effect on how it decrypts.

Long story short I decided against the full clone since I read it often doesn't work anyway, and tried mounting the drive. I'm using a hex reader to recover what I can from the unencrypted container and then I'll try letting truecrypt attempt to recover the file structure (don't want to risk further corruption if recovery fails).

Thank you for chiming in. I'll be changing my backup strategy so hopefully if this ever happens again I won't need to recover anything, as my backup won't be a month old.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Wed Jul 04, 2012 8:52 am

BaconatedGrapefruit wrote:Thanks for the input!

I don't think it'd be possible to use a different size drive for my needs, as it was a truecrypt encrypted drive, and the only way truecrypt knows where the backup header is located is by counting the byte offset (it appears as random data until it inputs the password you enter). As you suggested I probably could use a hex editor to manually copy and paste the end header, but I don't know if changing the number of sectors in between the header would have an effect on how it decrypts.

Long story short I decided against the full clone since I read it often doesn't work anyway, and tried mounting the drive. I'm using a hex reader to recover what I can from the unencrypted container and then I'll try letting truecrypt attempt to recover the file structure (don't want to risk further corruption if recovery fails).

Thank you for chiming in. I'll be changing my backup strategy so hopefully if this ever happens again I won't need to recover anything, as my backup won't be a month old.


You can clone a bigger drive unto a smaller one. All you need to do is to leave some unalocated disk space by deleting or shrinking a partition, but ofc the unallocated space must be enough so that the space of the source drive is equal or smaller than the space of the target drive. Unallocated space won't be taken into account when cloning.

With Windows 7 you can modify partitions without 3rd party programs. Just go to Control Panel>Administrative tools>Computer Management>Storage>Disk Management. You will figure it out from there, it's quite intuitive.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Wed Jul 04, 2012 2:26 pm

derFunkenstein wrote:..Even models in the same family have slightly different sizes as gb per sq.in. increases.


What?? 1 trillion bytes = 1 trillion bytes. I doubt he's referring to the actual physical size.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Wed Jul 04, 2012 2:41 pm

What the guy before me has said. You don't need matching disks to clone them. Get any 1 TB disk and you're done.

Edit: I noticed you have special needs and now wonder why you don't want to write to the original drive.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Thu Jul 05, 2012 8:21 am

Jason181 wrote:
derFunkenstein wrote:..Even models in the same family have slightly different sizes as gb per sq.in. increases.

What?? 1 trillion bytes = 1 trillion bytes. I doubt he's referring to the actual physical size.

Nobody said anything about physical size. Density of the platters is measured in gigabits per square inch; the platters don't change physical size, but the number of bits they can hold does. Variations in platter density can cause the capacity of a "1TB" drive to vary slightly between models and manufacturers. They will all be *approximately* the same capacity, but may vary by a few MB one way or the other.

To the OP: If the backup header truly needs to be at the physical end of the drive, then yeah you will need an identical drive, or you will need to manually copy the backup header with a low-level disk editing tool. Are you certain that this is an absolute requirement? Because if it isn't, using a larger drive should work.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Thu Jul 05, 2012 9:19 am

just brew it! wrote:To the OP: If the backup header truly needs to be at the physical end of the drive, then yeah you will need an identical drive, or you will need to manually copy the backup header with a low-level disk editing tool. Are you certain that this is an absolute requirement? Because if it isn't, using a larger drive should work.


I am thinking that his exacting requirements is because the use of Truecrypt and that because the header is trashed he cant read whats on the drive because of the encryption. But thats just my guess.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Thu Jul 05, 2012 9:22 am

just brew it! wrote:Nobody said anything about physical size. Density of the platters is measured in gigabits per square inch; the platters don't change physical size, but the number of bits they can hold does. Variations in platter density can cause the capacity of a "1TB" drive to vary slightly between models and manufacturers. They will all be *approximately* the same capacity, but may vary by a few MB one way or the other.

Said better than I, thanks for clarifying me. :D
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Thu Jul 05, 2012 6:52 pm

Like I said, I decided against getting another drive since they cost twice as much as when I bought them 2 years ago. I did image the drive on a 3TB, but didn't clone it or copy the image to another 1TB. I was able to restore the key from the embedded backup but so far I have been unable to make the unencrypted partition readable. I'm running a different data recovery app every night and I think I'll end up getting everything lost since my last backup. It's kind of frustrating no single recovery app seems to get every file type, and I haven't used one yet that restores file names and folder structure. I'm not too concerned, it'll just mean I'll have to spend a weekend determining what's what and renaming and sorting the recovered files.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Fri Jul 13, 2012 10:17 am

just brew it! wrote:Nobody said anything about physical size. Density of the platters is measured in gigabits per square inch; the platters don't change physical size, but the number of bits they can hold does. Variations in platter density can cause the capacity of a "1TB" drive to vary slightly between models and manufacturers. They will all be *approximately* the same capacity, but may vary by a few MB one way or the other.


First of all, the "physical size" of the actual data area would change with gigabits per square inch, but neither measure has anything to do with whether a terabyte hard drive will clone to another.

Even *if* the drives had slightly varying sizes (which I actually doubt), I'm sure that you could force them to the same size by fdisking the second one to exactly match the first.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Fri Jul 13, 2012 10:36 am

Jason181 wrote:Even *if* the drives had slightly varying sizes (which I actually doubt), I'm sure that you could force them to the same size by fdisking the second one to exactly match the first.

BaconatedGrapefruit wrote:The embedded backup header is a known offset from the end of the physical drive

Fdisk does not change the number of raw blocks on the drive. If the header is truly at a fixed offset from the end of the drive, changing the partition table will not help if the drives have different block counts.
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Re: Is 1TB = 1TB? Need drive EXACTLY the same size.

Postposted on Wed Jul 18, 2012 7:36 am

Just use DD from any Linux live CD to do a raw byte-for-byte copy. You *should* be just fine with a drive of equal or larger size. The offset should be based from the beginning of the disk, so a larger disk should not affect anything.
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