3 2TB drives cleared and reaady to go...


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I guess this is why I stick with what I'm use to. My system is now a 12 drive system holding all WD Black drives. pre-clear multiple times and no problems. Very positive about using these solid performers.

 

What problems arise if you don't preclear? So far I've not precleared any of my drives. I just let the array go down with the unRAID server clears them.

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What problems arise if you don't preclear? So far I've not precleared any of my drives. I just let the array go down with the unRAID server clears them.

 

unRAID doesn't preclear, unRAID formats the disks.

 

preclear helps test a disk prior to adding placing your data on that disk. Some disks (even new ones) are bad right out of the box. preclear will help determine if that is actually the case. preclear is not the end all, be all for ensuring a disk is not going to fail. Just like unRAID is NOT a backup system. It's a little more peace of mind. In regards to both of my statements, actually.

 

In your case, I would not run preclear now that the disks are in the array. But when/if you add new disks, running preclear is not a bad thing to do. A 2tb disk should complete in about 30 hours, fyi.

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unRAID doesn't preclear, unRAID formats the disks.

More accurately, if you have a parity drive assigned and are subsequently adding a new disk to your array unRAID will first clear the drive by writing zeros to it.  It does this while the array is off-line. (you cannot get to your existing data while it is clearing a drive.  It takes 6 or more hours to write zeros to a 2TB drive, so expect an extended down time when adding a disk that was not pre-cleared.)

 

After you start the array, unRAID will format a newly assigned disk after YOU press the "Format" button that is then visible.

 

unRAID makes no attempt to verify the zeros it wrote are subsequently readable.  Typically, the disk will not be read until after you load it with your files and then subsequently perform manual a parity check.

 

Joe L.

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To add even more info, the preclear script does a read, then it writes all zeros to the disk then it reads it again. The pre-read is so the drive firmware can map sectors that could not be read. Then, during the write state those sectors would be reallocated to a new spare sector. The final read confirms that the drive is reading back all zeros. This is a good test to exercise the drive before installing it and having it fail during the initial unRAID clear or fail while rebuilding an existing data disk onto it.

 

So, it should be considered a burn-in test that makes the drive ready to use in unRAID.

 

At the end of the day, the preclear script or the unRAID clearing process both make the drive ready to add to an existing array. The pre-clear script is just a very powerful tool that can be used outside of the normal unRAID process.

 

Peter

 

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