Why 'zero' a HDD other than security?

[videobruce]

Other then the probably most common reason to 'wipe' a drive of old data, are there any technical reasons to 'zero' a HDD?

[jaclaz]

5 hours ago, videobruce said:

Other then the probably most common reason to 'wipe' a drive of old data, are there any technical reasons to 'zero' a HDD?

Well, it is useful in some cases of data recovery, in the sense that for some time after a 00 wipe, deleted/de-indexed data will be easier to rebuild, but the effect is only marginal (and temporary, once the disk has been used for some time intensively, and possibly filled up there won't be many 00ed sectors anymore).

Another reason (not particularly relevant on modern disks) is that when wiping a disk you are write-touching (and verifying) each and every sector, so that possible "bad" sectors or areas that weren't detected as such by the controller will come up (and be replaced or excluded).

It has to be considered that, exactly because each and every sector is touched (and it is done sequentially, at the fastest possible speed, in a single session) it is actually provoking stress to the disk (just like restoring a dd-like image), it is a good idea, when possible, to make sure that the disk is cooled adequately (and if needed add a fan to keep it cool), with today largish sizes, a 00 wipe or a dd-like copy restore often takes several hours and for that long period of time the disk  is working continuously at the fastest speed possible, generating heat without the inactivity times that in normal operation would allow it to cool down.

jaclaz

 

 

[videobruce]

Does it matter if it's ones or zeros?

"dd-like image" ??

Edited January 10, 2023 by videobruce
added text

[jaclaz]

2 hours ago, videobruce said:

Does it matter if it's ones or zeros?

"dd-like image" ??

dd (which is the shortening of copy and convert , don't ask [1]) is a traditional Unix/Linux command that simply copies bytes (or in the case of hard disks sectors/blocks) as they are.

Of course there are several other programs that do the same, either command line or GUI.

dd-like or "forensic sound" means that the output (be it an image or directly another device) is EXACTLY the same as the input, i.e. it is an EXACT, 1:1 copy.

For whole disks, it means that the target image (or the cloned disk) is exactly the same size as the source, as it contains all sectors, unlike many (commercial) cloning/imaging tools that - in order to save time/space - either interpret the filesystem and only copy files indexed in it or (swiftly?) ignore already 00ed sectors in the source, usually adopting proprietary file formats for the images (an image taken with dd is usually called RAW as it contains nothing but the contents of the source, no headers, no footers, no checksums, etc.).

About 1 or 0's it doesn't really matter, the 00 is a convention, new disks (usually) are all 00's, if you want to check at the bit level the values used are (normally) 55 and AA hex, i.e.

01010101

10101010

so that (in two passes) every bit is actually flipped.

jaclaz

[1] If you need to ask, and have some time, enjoy:

http://reboot.pro/index.php?showtopic=15207

 

Edited January 10, 2023 by jaclaz

[videobruce]

I won't ask why not cc. (The link in that link on that question was dead.)

Edited January 10, 2023 by videobruce

[jaclaz]

Fact is that noone really knows for sure, some versions are plausible. others not so much:

https://unix.stackexchange.com/questions/6804/what-does-dd-stand-for

jaclaz