shredding decreases Hard disk drive life span.

voidshot

New Member
I found this article that talks about why shredding more then 6-8 passes can be detrimental(bad) for your hard disk drive "read-write" life span

Why shred a file with more than one pass? Because the hard-disk can be removed from the casing and the physical evidence of the data may still be visible under a microscope. Multiple passes will make this very difficult, or impossible.

Now, why not shred away? Because everything in the hard-drive wears out; The reader arms, the motor, the read heads, the steel disks. Everything has a limited amount of acceptable wear. You may have read that Portable flash drives have around 1000 read-writes before the media becomes unreliable, but hard drives have the same limitation (although you get many more read-writes before it becomes useless).

A hard disk accesses data in a linear fassion, like a CD or DVD. The read-heads start at the center and move outward until the data is reached, then it begins to read (the seek process). If you access a point that has already been passed, the process starts over. If you access files out of order, of write over a file multiple times, the seek process starts over.

At around 4 passes, a file should be completely unrecoverable. The US government has a requirement of something between 6-8 passes when this method is acceptable. (For very technical reasons, the disk is physically destroyed when very sensitive data is involved.)

Anything more than 6 passes is an incredible waste of time and HDD life. If you are really paranoid, the best thing to do encrypt the disk before using it. This is the only way that a full disk wipe will be useful anyway.

QUESTIONS:
1.so is it wise to use gutmans(35 pass) shredding? i think it should only be used for extremely sensitive data like bank account information
this would also mean that unused space wiping should not be done on a regular basis unless its crucial, like when giving your computer to a technician to fix it or sending it back to the factory to fix up something, or simply letting a friend borrowing your lap top and his the kind that knows his way around a computer and just loves to be on peoples dirty secrets or private manners

2.will erasing a 1GB file with 35 passes(gutmann) have the same detrimental effects on my HDD read-writes compared to when i erase a 10MB file with 35 pass(gutmann)?

to make the question more clear, lets say i erase a 10mb file and a 1gb file using the same 35 pass method(gutmann) will both of them have an equivalent detrimental effect on my HDD read-write life span? or is one greater then the other? i think the 1gb 35 pass would impact the the HDD life span more, right?
 

DavidHB

Active Member
There is a companion forum on data forensics; you will find much of the information there surprising. With a modern hard drive (certainly any SATA drive, and probably all IDE ones made in the last few years also), a single pass over-write/shred is sufficient to make the data un-recoverable for any domestic or commercial user. If anyone has found a means of recovering such files, they have not made that fact public.

It is true that all drives wear out (so always keep backups); it is also true that disks are designed to have a reasonable lifespan. A three year MTBF is a reasonable conservative guide. More disk activity will increase wear, but I don't think that the process is either linear or well documented; drive failures are often quite unpredictable. Obviously, if you don't need to use the Gutmann method to be secure (and even Peter Gutmann is quite clear that you don't), then there isn't much point in using it. I use HMG 3-pass for erasing files and folders and the default single pass for wiping free space; wiping in particular takes much too long if you use anything more than a single pass on a large drive.

I think that the article you quote is somewhat overstating the case, but is on the right lines. The truth is that, for normal security and privacy, erasing sensitive data that is no longer needed and wiping the drive before you sell or dispose of the computer will be sufficient to turn the attention of any snoopers elsewhere. As regards hard disk life, I would not expect file/folder erasing to have much of an effect. A free space wipe is quite demanding, but, as you won't do it that often, it too will probably not increase wear. What it may do is push a hard disk that is already failing over the edge. That, as I said, is what backups are for.

David
 

Joel

Active Member
Wipes will cause problems only because of the following factors:
  • Drives have a negligible, but non-zero, error rate (last I checked, it was something like 1 in 10^14 bits on average or something to this effect, which is, one data error every 11TB of data written)
  • Mechanical failure by the failure of the spindle motor (the motor which physically spins the platters)
  • Mechanical failure by the failure of the disk head arm (the drive head which reads the magnetic signals on the platters)

Point 1 is unavoidable, 11TB isn't fantastically high, but erasing definitely increases the chances of these events happening. This is not totally unexpected -- that's what software checksums are for, and file systems usually have mechanisms in place to overcome this problem and reduce the error rate further (I'm not sure whether the hardware CRC employed will rectify such problems)

Point 2 is also a minor point: The platters of your drive spin at a constant linear velocity (5400 rpm, or 7200 rpm, EXCEPT for some WD drives with some adaptive spin rate algorithm) and for as long as you are using the drive, the motors are on. The only time the lifespan of the motor can be lengthened is when the drive is turned OFF, which is when your system goes into standby. Erasing/wiping takes time, which may deprive your computer of the ability to go into standby and thus lengthening the lifespan of the drive. In any case, these motors are quite durable.

Point 3 is the most likely cause of drive failure. This is where the motor is stressed by start/stop actions WHEN the user causes drive seeks. Every time the drive needs to access a portion of the drive where the disk head is not at, the disk head must physically move, maintaining that the distance between the arm and the platter (fly height) is just a few microns above the disk platter. This is the process of seeking. This is also why random accesses on a hard drive is slower than e.g. flash memory. Seeking is a mechanical action. The start/stop processes causes the arm and the corresponding motor to be under high stress. This doesn't mean that the stress cannot be lowered. Continuous motion will put the drive head under significantly lesser amount of stress. That's why I recommend that users do not use the computer during the free space erase process, and also why I advocate NOT running more than one erase at one point. It slows down your erase process, and places unnecessary stress on the drive.
 

voidshot

New Member
oh i see, so its a bad idea to be doing to many unnecessary shredding passes and to many unused space wipes: got it, only for crucial data and moments for sure.

also, does this mean that anti virus scanners or any type of system scanning has the same effect on the HDD read-write life span like shredding does?

PS, I'm pretty sure that a user with a SSD(solid state drive) like flash drive or dram drives have absolutely nothing to worry about with the read-write life span being detriment'ed by unused space wipes and shredding since the drive is static and does not require heads. is this assumption correct? or do this drives get wared out as well with each unused space wipe and shredding?
 

Joel

Active Member
voidshot said:
oh i see, so its a bad idea to be doing to many unnecessary shredding passes and to many unused space wipes: got it, only for crucial data and moments for sure.
Basically, it's up to you to weigh your risks. HDDs are cheap now.

voidshot said:
also, does this mean that anti virus scanners or any type of system scanning has the same effect on the HDD read-write life span like shredding does?
Yes, same thing.

voidshot said:
PS, I'm pretty sure that a user with a SSD(solid state drive) like flash drive or dram drives have absolutely nothing to worry about with the read-write life span being detriment'ed by unused space wipes and shredding since the drive is static and does not require heads. is this assumption correct? or do this drives get wared out as well with each unused space wipe and shredding?
SSDs will have the same problem, but a different cause. SSDs have limited write cycles. DRAM drives do not have the problem. In any case, SSDs just need a single reset to eradicate all traces of information.
 

voidshot

New Member
so Dram's would be the ultimate drive to go for?, for its lightning speed, endurance, and wiping methods.

1.could you delete certain individual data/files on SSD's or Dram as apposed to having to format the entire drive just to get rid of something?
2.do SSD's and Dram have recovery methods, meaning, when files are default deleted are their stored in free space like in HDD's and capably of being recovered with recovered programs? or their permanently deleted for ever?
 

Joel

Active Member
voidshot said:
so Dram's would be the ultimate drive to go for?, for its lightning speed, endurance, and wiping methods.
DRAM by definition loses its charge after a few clocks, which makes all its data irrecoverable. I vaguely remember a paper published which claimed that they could get information off a discharged DRAM module, but I can't remember who wrote it, or if it was corroborated.

voidshot said:
1.could you delete certain individual data/files on SSD's or Dram as apposed to having to format the entire drive just to get rid of something?
I'll ignore DRAM for reasons above. SSDs just need to be reset to "off" (IIRC) by the TRIM command in ATA.

voidshot said:
2.do SSD's and Dram have recovery methods, meaning, when files are default deleted are their stored in free space like in HDD's and capably of being recovered with recovered programs? or their permanently deleted for ever?
Yes, since they store data. Hoewver in the case of SSDs the order may be jumbled due to wear-levelling mechanisms.
 
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