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i just got a new WD Red 6 tb drive and is about to install it and was wondering if it is recommended to preclear it before use and if so how should I do it? It seems that the support of the preclear plugin is broken in recent updates


if I shouldn’t preclear does there exist a plug-in I can use to test the drive before use? 

Edited by fc0712
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If you have the Community apps plugin installed, search for preclear and you will find the plugin.  


Now, I have used the plugin many times over the years and have never had a problem with it.  But let me say a few things.  I have a simple NAS system.  I never installed the 'optional' Statistics package (which phoned home).  I do not run the unassigned devices plugin.  I have never attempted to clear more than one drive at a time.


Since I have not done a preclear in a few months, I just started one to see if it still works with the latest version of unRAID.  (I have an old Seagate ST3000DM001 that I use just for checking this plugin.)  It will take about a day to finish. I will report back if I have a problem with the plugin. 


Do you have to preclear with the plugin?   NO!    unRAID will now preclear the disk in the background, then format it, and add it to the array.  But if you would rather make sure that the disk you had to your array is working and without surface defects, you need test it before you add it. You can use the manufacturer's disk testing program and there are folks who do.  Those are your three basic options. 

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As Frank said above, feel free to use Preclear plugin for convenience if you like, but since its original purpose (minimizing downtime required to insert new drives) has been integrated into unRAID itself, I've stopped using it. A lot of people (myself included) continued to use it for a while to detect "infant mortality" in newly installed hard drives, but since the plugin doesn't seem to be supported anymore (regardless of whether it technically runs or not) we probably shouldn't even be doing that much.


Myself, to address the need to detect flaky drives on install I've been opening up the handy new web-based terminal window, starting a "screen" session, and issuing a badblocks command. This does much the same thing as the preclear plugin did; read/write the entire disk and compare with expected contents.


badblocks -nvs /dev/sdx will do a non-destructive test of the entire disk. If you don't care about the data on the disk you can do badblocks -wvs /dev/sdx.


Just my $0.02



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31 minutes ago, Ambrotos said:

Myself, to address the need to detect flaky drives on install I've been opening up the handy new web-based terminal window, starting a "screen" session, and issuing a badblocks command. This does much the same thing as the preclear plugin did; read/write the entire disk and compare with expected contents.



I believe you have to keep both the terminal window open until badblocks finishes.  Otherwise, it will be terminated.  Of course, this will also mean that you have to keep the PC up-and-running for the duration which will be some goody number of hours.  ?


EDIT:  Just realized that you said, you started a screen session.  That would allow the user to close to the terminal and re-access the screen session at a later time.  IF you are going to do this be sure that you have screen on your system.  The easy way to get in to install the Nerd Tools plugin. 

Edited by Frank1940
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3 hours ago, fc0712 said:



I’m in the process of running a smart extended test through unraid webgui, will that be suffcient to determine if the drive is okay? 

It's one half of the process, and should be enough to catch most problems. The long SMART reads every sector, but doesn't care what's there. After you add it to a parity protected array, it will have every sector written, so as long as it completes the process to add it without error, and passes a parity check with zero errors, I'd call it good.

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  • 2 years later...
  • 3 months later...

Was about to shuck 2x 14tb wd my books.

Thought I'd run preclear before I did.

One of them started ticking for a few minutes but seems to be running.


I'm only on the first pass though.

At least I know to be suspicious of it and if it does it again it's going back.


It's better to identify a faulty drive early and return it than it die later.


(Especially if it's been shucked out of a usb)


The ticking has stopped now so I'm not sure but I'll make sure I'm happy before I shuck it.


I think preclear adds random head movements so I'll wait and see what happens next. (Or maybe it was my plumbing making the noise)


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Man preclear is brutal.

I think it's killing one.

47c but still going at 215mbs

But it's ticking. I think it's bad.

Let's see if it lasts.

If this doesn't kill um I'd say they are good but I think that one is going back either way.

I've heard that noise before (20 years ago) and it's not good.

(As you might have noticed I'm new to preclear so I don't know if I should worry about the click (click if death maybe)) and i didn't bother with my last drives because they were new wd golds and the warranty is 5 years.


I'd possibly get no warranty if I shuck them so I'd need to feel confident.

These will be my new double parity if I can trust them.

Edited by mdrodge
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  • 11 months later...

I ran a preclear script years back on some 2TB and 3TB drives I've added. Glad I did. Found one that had issues during the write/read/verify. Afterwards I ran a SMART test in my windows machine and verified the drop in health. I RMA'd that sucker just a few days after receiving it. The replacement passed and I've been error free since, but have never had an error on any drive. I have nine drives now since I started with a couple a decade ago. I plan on getting a 4TB and replace my 3TB parity drive to accommodate more 4TB drives. Currently I have a mix of 2TBs and 3TBs. Sometime later I'll get another 4TB to swap with my aging 2TBs. But I've always loved that preclear process to verify my purchase.

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