gfjardim had different goals for his script (quickest possible clearing, less stress on disks), that many users (myself included) found objectionable - we actually want to stress test the disks, not take it easy on them. This plugin ships by default with gfjardim's own pre-clearing script, and it needs to be noted that this is NOT the Joe L. Yes, there is a plugin named "Preclear Disk", by gfjardim. Unfortunately LimeTech has not seen fit to integrate a Pre-Clear function into Unraid, so you are still forced to use 3rd party solutions. Another benefit is that when adding a Pre-Cleared drive to an Unraid array, due to the presence of the Cleared signature on the disk, Unraid adds the drive instantly, without the long period of array downtime experienced when you allow Unraid to do this Clearing. Knowing that a drive is healthy before you add it to your array is a huge benefit that, as far as I am aware, is unique to Unraid. Running a Pre-Clear on all drives, even previously used drives from other devices, has become a best practice for Unraid. Adding more passes increases the processing time.
Unraid change disk number full#
if it would take 17 hours to read a full 8TB drive, then it will take 50+ hours to read + write + read the drive. Typically this default Pre-Clear script's config takes 3x's longer to process than it does to simply read the drive once - i.e. The script will even give the before and after SMART health stats, so you can see if a drive is tending towards a failure profile. A standard pass includes a pre-read, a write, then a post-read to validate the data (zeros) were written correctly. made his Pre-Clear script configurable to suit the goals of different users: you can do a simple one pass, writing the zeros and the signature the same as Unraid does, or you can go with multiple passes, as many as you desire, to really give a drive a workout. also recognized the anecdotal wisdom that HDDs most commonly fail either when brand new (manufacturing defects) or very old (wear and tear), and that he could turn his Pre-Clearing script into a stress test to validate that drives are healthy, and hopefully to cause new drives with manufacturing defects to fail early, before you add them to your array, and when returning them to the seller is likely easier. This also opened up the possibility of Clearing drives on a different machine, or simply clearing a stack of drives that you then store offline, waiting until you need to use them. By doing the Clearing outside the array, array performance would not be impacted during the Clearing. realized that he could write a script to do this Clearing routine before you even add the drive to your array.
Considering that simply Clearing a disk (writing zeroes) takes around 2 hours per TB, you can see that this is incredibly inconvenient especially when adding larger drives. When this last step occurs, because the drive has all zeroes, it does not alter the parity values that were previously calculated, as adding zero to a value does not change a value.ĭuring this drive clearing process, the Unraid system is in a reduced state of performance (Note: it might actually be that Unraid makes the array unusable during the drive zeroing - I've seen that mentioned, but it has been so long since I've allowed Unraid to clear a disk that I truly don't remember). Instead, it first "Clears" the drive by writing zeros to the entire drive, then writes an Unraid signature to the drive, then finally adds the drive to the available storage. When you first add a drive, Unraid does not make it immediately available for use. Unraid also has a great feature in that you can add additional drives at any time, expanding your storage. With dual parity, a different calculation is performed and written to the 2nd parity disk, so that two drives can be rebuilt at the same time. If a drive is replaced, that simple math formula can be reversed to rebuild the contents on the replaced drive. Unraid uses an unusual parity scheme: All the bits from the same position across all drives are added up to calculate a parity value, and that value is written to the same position on the parity disk.