When is zero out data justified?
Is it needed for a clean reinstall if the machine does not change owners?
iMac (21.5-inch, Late 2012), OS X Mountain Lion (10.8.3)
No.
No.
The only reason to ever zero out your hard drive is when you want to destroy the data residing on it, preventing anyone else from gaining access to it. It is absolutely not needed for any other purpose.
As others have stated, no. Some people still believe you need to do that to clear up bad blocks. That hasn't been true in a long time. Hard drive controllers do that on the fly, now, and there are very few "reserve" blocks to swap into. If you force it, you may use up all the reserve blocks, and when the drive detects a bad block, it cannot remap and the drive is done. However, once blocks start failing, there is usually an underlying cause which will eventually eat up the drive.
Than you Thomas. I still have some Windows habits, and one of them is to format my hard drive whenever something goes wrong with my computer. I know it's extreme but it's the only way I feel confident the problem is gone.
Hard drive manufacturers recommend the drive be "zeroed" erased before a operating system is installed and it also happens that's the approved method to remove bad sectors BEFORE laying data on the drive.
Western Digital says:
Writing zeros to a drive is recommended any time an operating system is to be reinstalled on a boot drive or whenever a blank drive is desired.
Seagate says:
The most common reasons to Zero Fill a SATA or ATA (IDE) hard drive are:
- to remove a virus that cannot be removed without destroying the boot sector.
- to change from one operating system to another and wish to remove everything from the drive.
- to erase confidential information for privacy reasons.
- to scan for bad sectors that can be detected and replaced with good spare sectors when writing to the sectors.
By design, modern disc drives maintain spare sectors for reallocation purposes. Usually, sectors become difficult to read long before they become impossible to read. In this situation the actual data bytes in the sector are preserved and transferred to the new spare during a sector reallocation. Similarly, when a disc drive writes data (like a zero fill erase procedure) and encounters a problem, the drive firmware retires the problem sector and activates a replacement before giving successful write status.
http://knowledge.seagate.com/articles/en_US/FAQ/203931en
There is indeed a mechanism in place to map off failing sectors as a user uses the computer like normal, however it is NOT always in effect and it's not perfect because if the sector fails completely the data can't be recovered and moved to a spare sector as it can't be read at all.
I've found instances of live partitioning where Disk Utility won't create another partition unless I ran a Zero Erase on the free space, then it worked just fine.
I've also found if OS X is installed over a bad sector that may have issues or fail to install, or boot successfully, regardless how many times I reinstall it. Until I do a Zero Erase using Disk Utility then it magically works fine.
So since two of the leading drive manufactures RECOMMEND zero erasing a new hard drive or a existing one before a operating system is installed, I tend to believe them and recommend this procedure for anyone reinstalling their operating system on their hard drives or using a hard drive for the first time.
SSD's don't suffer from bad sector issues far as I can tell. 🙂
Barney-15E wrote:
As others have stated, no. Some people still believe you need to do that to clear up bad blocks. That hasn't been true in a long time.
It is still true today, despite the auto-mapping off ability as it's not always in effect, like when the operating system is being installed.
and there are very few "reserve" blocks to swap into.
I haven't check exactly what percentage are spares, but I would assume the larger the drive same percentage thus more spares.
If you force it, you may use up all the reserve blocks, and when the drive detects a bad block, it cannot remap and the drive is done.
Bad blocks don't just disappear if you ignore them, eventually they will rear their ugly heads and it's a lot better to know in advance when one can return the drive under warranty or get a new one before it dies later and they have to perform expensive platter dissection to get their files back.
However, once blocks start failing, there is usually an underlying cause which will eventually eat up the drive.
Bad blocks come from the factory and they occur over time without the drive actually failing.
However a excessive amount of bad blocks detected on free space can certainly give a heads up the drive is malfunctioning or been subjected to shock damage and needs to be replaced.
So it's not that if one gets a bad block the drive is failing, it's more like they have to have a whole lot of them and usually a zero erase will fail as all the spares are used up, thus giving one the heads up it's done for.
daemon1277 wrote:
Than you Thomas. I still have some Windows habits, and one of them is to format my hard drive whenever something goes wrong with my computer. I know it's extreme but it's the only way I feel confident the problem is gone.
I recommend bootable clones and if you do have a problem, to zero erase the partition from the clone to eliminate bad sectors and then reverse clone.
Most commonly used backup methods
It also happens to do a excellent defrag in the process.
I still have some Windows habits, and one of them is to format my hard drive whenever something goes wrong with my computer. I know it's extreme but it's the only way I feel confident the problem is gone.
Sometimes, that's necessary on the Mac as well. (Though, if you do it every time there's a problem, you'll end up wasting a lot of your time, as it's not necessary for most problems.) However, even when it is necessary, there's no reason for zeroing the hard drive. Just erasing is fine.
Failing sectors will not be found by writing zeros any faster than it finds them writing ones. If you zero out sectors sequentially, then a failing sector that has not failed when the zero is written will not be remapped until you try to write actual data. If there are no spare sectors left because you wrote useless zeros to an actual bad sector further down the line, you have removed one possibility to save the useful data.
Yes, you may have remapped a sector down the line, but if your real data cannot be written because there are no open reserves, you have lost data.
When is zero out data justified? Is it needed for a clean reinstall if the machine does not change owners?
