Hello,

 

I'm giving Unraid a trial.  I've been lurking for a while and have read many references to the preclear script, I understand it's purpose for hot spares, but for a brand new array with brand new drives, it seems like it would also be a good idea?

Hello,

 

I'm giving Unraid a trial.  I've been lurking for a while and have read many references to the preclear script, I understand it's purpose for hot spares, but for a brand new array with brand new drives, it seems like it would also be a good idea?

 

Preclear is not just for spares; it's a very nice stress test for disks. I always recommend to run it on every new disk drive.

Yes, preclearing new drives is a good idea. Hard drive failures follow the bathtub curve.  Lots of failures early in their life (if exercised properly), much lower during the expected useful life of the drive after the initial tests, and then after the expected life the failure rate goes up.

Hello,

 

I'm giving Unraid a trial.  I've been lurking for a while and have read many references to the preclear script, I understand it's purpose for hot spares, but for a brand new array with brand new drives, it seems like it would also be a good idea?

Actually, for a "hot" spare, as in, a disk that would be used to replace a failed disk, the preclear script only serves the same purpose it does for any other new disk, which is testing. A replacement disk doesn't really need to be clear. Only disks added to new slots must be clear so parity will remain valid.

 

Always test new disks because every bit of every disk is required if one of them fails.

Thanks guys.  Using preclear is not part of the getting started guide for 6 that I'm following so how do I proceed?

I installed the plugin and the original script from this thread.  My parity check is currently running.  Guess I have to delete the parity and data drive I have set up so far and run preclear on them once they're back to being unassigned.

 

 

You don't need preclear to setup an array. If this is a new one, it will just format the drives, set parity, and off you go.

 

The issue really is, as mentioned, adding drives. If you don't preclear, then when unraid formats the new drive, it will go through the entire thing and set it all to zero, and then allow you to start using it. The catch is, this can take HOURS. That means HOURS that your array isn't accessible because its working on adding your new drive (assuming i'm remembering this right).

 

If you are just giving unraid a trial, it probably doesn't matter. But when you have a 10TB array and you want to watch movies, you don't want to wait. Adding a precleared drive only takes a few mins, so its much easier.

 

But, if you want the full unRAID experience, you should try out preclear. And if you put data you care about on the array, doing the preclear as a burn in test for your hdds is also highly recommended.

 

f you put data you care about on the array, doing the preclear as a burn in test for your hdds is also highly recommended.

This, exactly, for several reasons. Not least of which is the lack of QC on new drives. In regular computers, a bad bit here or there, especially near the end of the drive, may never even be detected, or matter much. Unraid single drive failure reconstruction requires ALL the bits on ALL the rest of the drives to work perfectly, so a full surface test is the only way to be sure your data will be ok.

 

Preclear exercises the drive the same way unraid will use it and provides reports that can give you confidence in the drive.

I'd like to check an old HDD for bad sectors. I read somewhere that modern harddisks has spare areas to automatically replace any bad sectors. Can preclear find bad sectors and permanently avoid them in future writes? Or use other softwares for that?

I'd like to check an old HDD for bad sectors. I read somewhere that modern harddisks has spare areas to automatically replace any bad sectors. Can preclear find bad sectors and permanently avoid them in future writes? Or use other softwares for that?

 

Yes, preclear exercises the drive so it should remap bad sectors.

Great. Thanks for the info.