How and why to PreClear your hard drives before adding to your array

[@codythomashunsberger]

As someone brand new to Unraid, this channel is just awesome. Thanks for all the hard work to help out us rookies

[@petethompson2715]

I just wanted to say thanks for all of your videos. I am new to unRaid and your videos have really helped me customize my setup with some great plugins and apps. You are my go-to now for unRaid.

[@SpaceinvaderOne]

Thanks. Glad i could help Pete. Best of luck with your server :)

[@soulman1949]

Another excellent video. I've watched countless videos on setting up unRAID and not one has mentioned PreClear, which is obviously a very important step. Thanks again.

[@SpaceinvaderOne]

Yes always best to preclear the drives :)

[@stevegerst5229]

Sense the preclear plugin is depreciated is there a different way to preclear a new disk or is preclear not nessasary any more above version 6.4? Most importantly thank you for all the videos!

[@jbyrne8977]

Might be worth adding a note about the plugin vs docker version of this. As the apps page has changed and docker doesn't follow the same process

[@joker927]

Very helpful, including the extra information for context. Bravo.

[@bugsysiegals]

I've 3 x 8TB drives which are being pre-cleared. They're taking a long time but I'm happy to make sure they're good drives. That said, I've seen some recommendations to do pre-clear 3 times!! If I do this 3 times, and it finds bad sectors, etc., will it know to reallocate data away from these sectors and thus reduce the chance of disc failure or URE's when rebuilding in the future? What's my advantage of taking another 3 days to run 2 more pre-clears? This is for movies and tv shows for Plex but I'm more than happy to be patient and run pre-clear 3 times if it helps to reduce the chance of disc failure or to identify something which allows me to warranty the disc.

[@andrewraynor2685]

Another excellent video and very informative thanks and keep up the good work!

[@SpaceinvaderOne]

your welcome. Glad its useful!

[@tshepp89]

Thanks mate. Still loving your unraid vids.

[@Polopollo75]

This plugin doesn't work anymore and it looks like it's the way it goes for now. What other plugin do you recommend to run before clearing a disk to test its bathtub curve? :(

[@RobertBullock]

I used to use a utility to scan all the sectors on my Mac to test for bad sectors and SMART also would give errors but I'm just going to use preclear instead of that. I still like preclear as it would let me know before the drive is even added to the array. Peace of mind, IMHO, even though it's deprecated. I've got two older drives to add (datacenter hand me downs I'm guessing) so I'm running extended SMART tests and preclear on them. Have all sorts of different ages and models in mine, with dual parity and only 8 disks total so, seems safe enough.

[@papayou76]

Thank you for your work and all your efforts. Continue !

[@iveo83]

Thank you for all your videos they have been an extreme help for me! Anytime I ask on forum or reddit for help someone gives me a link to your vids lol

[@1kyleabc]

What happens if you were to lose system power during a PreClear? Does ZFS also use a "PreClear"-like function when adding new disks/pools?

[@paulgysen7323]

Thanks for your great tutorials!!! I have a question which I can't find the answer to... New to Unraid but not new to a pc (using it since 1986) so my question is the following: Can you use a new HD out of the box or do I need to create a partition on it first and then PreClearing? If so, what kind of partition table do I use? Does Unraid create the main partition after PreClear and/or during format? Thanks for your reply and your tutorials ;-)

[@hydranmenace]

I don't understand what the advantage to preclear is. Unraid will zero and clear the drive when you add it to the array right? Then it allows it to be added? You mentioned that takes a long time. But preclear also seems to take a long time, so what's the difference between letting unraid do it or preclear doing it and adding that signature? I could see preclear being advantageous if it were faster. What am I missing?

[@MostlyDrew]

This is how i understand it; yes both processes look like they take the same amount of time. The difference is, if you let unraid clear the disk, your array with be down during that entire time it is being cleared. However, if you let the pre-clear program clear it, you can have your array still online while the disk is being cleared. Then when adding the disk to the array, its a matter of seconds. TL;DR unraid clear: array is down while clearing. Pre-clear: array is still online while clearing.

[@scorpian007]

I'm finding that preclearing disks ALWAYS crashes unraid at some point through the write process. Doesn't matter if its a new or used disk, it's incredibly frustrating.

[@ianwoodrow6595]

Quick question for you if you could guide me in the right direction? All my drive bays are full and used in the array, I want to upgrade a 4tb to a 10tb, my question is should I pull the 4tb out, stick in the 10tb, preclear it and then add it to the array? or is there another way I should do it?

[@DougCube]

What is the difference between the dropdown options: "Clear" vs "Erase and Clear the Disk"? (Googling this did not help.)

[@ierosgr]

Old post but I am going to give it a try. Happened to notice that in your example you are using a 1Tb Disk. I myself happened to use sas drives of 1.2Tb and the pre-clear process went smooth. Yesterday I needed to check a 4Tb drive and it was then that I notice the pre clear script creates a partition of 2Tb and the other is left intact . Does this means the script only checks a portion of the disk an not all of it? Does it depend from something? PS The disk was empty - war with no partitions or anything on it.

[@ievmertus2486]

Video content still is all useful and applying in 2020.

[@alexpowell7977]

great video lots of information, I am planing on adding a SSD as cache drive, does this have to be preclear before hand?

[@SpaceinvaderOne]

Hi, Alex. Personally I wouldn't preclear an SSD for cache.

[@alexpowell7977]

great many thanks love the unraid videos

[@ariele-paolomaesano3180]

What if you create a new array? do you need to preclear the parity drive and then add a drive one by one after preclearing them?

[@bunnster22]

Just tried to pre-clear two brand new WD Red 4TB drives. I have speeds as slow as 5MB/s. Tried updating my LSI HBA firmware to the newest IT mode and still nothing. My UDMA CRC errors are showing over 122,121 counts. Something is really wrong and I've got no clue what it is anymore.

[@chris1benassi822]

bunnster22 try different cables, different sata port. Could be anything. Did you check the unraid forums to see if this is normal behavior for a WD Red? If it was a blue or black series I would worry and probably return them.

[@SpaceinvaderOne]

Hi yes, you shouldn't be seeing those errors. Like chris1benassi says check all of your cabling as this can cause issues, then seeing UDMA CRC errors.

[@-rhys]

Hugely useful video. Thank you.

[@SpaceinvaderOne]

Your welcome, Rhys.

[@shockracer]

Thanks for all your informative videos! Quick question on Preclear, my server is full with drives, should I leave the array down since it will be missing a drive while I Preclear or can I start the array ?

[@drmetroyt]

Drive will be unassigned drive if the drive is new and not added to disk .. in this case you can safely use the array

[@onitramt77]

Thanks again for a great vid!

[@drewbuntoo]

"PLEASE NOTE THAT THE PRECLEAR PLUGIN HAS BEEN DEPRECIATED FROM UNRAID 6.4 ONWARDS." is preclearing no longer required? is it automagic?

[@SpaceinvaderOne]

Well some people think its not needed. But I have had a few brand new drives that have failed during preclear so i was very pleased to have used it. What to do for now is to add the drive to the array and unraid will clear it (different to preclear) then straight after run an extended smart test on the drive. this is the next best process IMO

[@shishirxs]

is it possible and safe to preclear multiple drives in same time ? requesting you to let me know !

[@doozowings4672]

I'm sort of confused, the binhex preclear now runs in docker, is that correct ? Did it change or do Have the wrong preclear >?

[@kevincinalaska2551]

Good Sir, question here. :) Is there a way you can point me to that I can PreClear a new unRaid setup where I have not created an array yet? Just some new HDDs.

[@SpaceinvaderOne]

Yes. You can install the community applications plugin. Then afterwards search for the preclear plugin and install. You then can preclear your drives before you have even made an array :).......(plugins can be installed and run without an array)

[@kevincinalaska2551]

Thank you. I have all 4 of my drives currently going through a PreClear. It was kind of you to respond to my question. Cheers! :)

[@jaketrullinger9370]

I heard you discuss needing to preclear on new disks vs replacing an older data disk. But, should I preclear a new drive if i'm going to use it to replace my previous parity drive? Moving from a 4tb to a 10tb parity disk, while also replacing an old 500gb junk drive in the array with a 10tb drive.

[@SpaceinvaderOne]

yes make sure you preclear a disk you will use for parity. We preclear just to stress test the drive. When a drive is new it is one of the common times it will fail Preclering just helps us see if this is likely to happen with our drives. Last thing you want is the parity failing then you having to rma it back and replace it.

[@WineCountryFlix]

if you have more than one to preclear do you do one at a time or all at the same time?

[@SpaceinvaderOne]

You can do them all at once.

[@WineCountryFlix]

@@SpaceinvaderOne thank you I did do that 5 20TB disks 17.5hours in and 75% done. Not bad I was thinking like a week.

[@EponymousBargain]

Any reason why my the zeroing phase is taking longer? Pre-read was about 115 MBps. But the zeroing phase is about 24 MBps.

[@SpaceinvaderOne]

Zeroing will always be slower as write speeds are generally slower than reads with most drives :)

[@sandspatel]

Do you recommend doing this before first building an array, or can you perform this type of check on a previously built array?

[@SpaceinvaderOne]

This must be done before building an array. The check will erase (zero) the disk. So if you have the array already set up just use preclear before you add any new disks.

[@sandspatel]

+Spaceinvader One +Spaceinvader One thanks will do. Another question for you. I'm planning to setup my first unraid and am thinking of whether to use single parity with a warm spare or dual parity topology. Do you have any tips?

[@SpaceinvaderOne]

I think it depends on how many data drives that you have in the array. The more drives you have the more chance of more than one failing. I would say if you have 6 or less single parity is fine. However, if the warm spare you would use is as large as the parity then I would use it as a second parity. Why? Well just because if it's in the server anyway, you might as well have it there giving some protection. Not just sitting there. Should a drive fail the contents will be emulated anyway. So you could just buy another drive if there is a failure. Yes, you can't rebuild the array so quickly but as you have 2 parity drives then you could still lose another drive and still be able to recover so this isn't such an issue.

[@sandspatel]

+Spaceinvader One Thanks. I think it's always nice to have the extra redundancy but if rebuilds are likely to take a performance hit then 1 parity drive should be sufficient for my needs right now as long as I'm taking regular backup snapshots. Especially as normally mechanical drives will usually give some indication of poorer performance before failing. I'll have to keep an eye out for those SMART scores! Thanks again ..and great work on the channel really informative stuff!

[@SpaceinvaderOne]

Hi Sandeep, No, I didn't mean the rebuild speed would be slower with 2 parity drives. I meant it would be slower as you wouldn't have the replacement drive already prepared. You would have to purchase one then preclear it to test it. But the actual rebuild process would be the same.

[@DJparsons89]

PreClear is not an app in the CA! how do we get it now?

[@Rmilyard]

I started to play with unRAID today and I also can't find it.

[@JustARandomSomething]

If i plug a drive in that contains old data, do i need to format it first and then pre-clear OR will the pre-clear format it for me.

[@JoeAnshien]

clearing your drive will overwrite whatever you had with 0s

[@Mike-vb6qw]

Are suppose to be able to use the array i.e., play a media file while preclearing a new drive? I tried this and the Preclear operation stopped and I had to manually reset my server.

[@SpaceinvaderOne]

Yes you can use the array when preclearing a disk. How many drives were you preclearing when this happened..just the one or multiple frives?

[@Mike-vb6qw]

Just one new 8TB drive. I did turn off the web GUI so I could take my lap top into the theater but did not turn off the server/HTPC. When I logged back into tower on my laptop that is when I noticed that it was not showing the new drive in "tools". This was after launching Splashtop. I am using a new sata LSI 9211-8i controller card in IT mode for the first time but that all seems to be working.

[@Mike-vb6qw]

I tried it again and Preclear stopped as soon as I launched the Windows 10 VM. I have posted my issue on the Preclear thread.

[@hamzaafandi9293]

i actually have my hard drives and am just waiting for my server before I setup everything. is there any way to preclear disks before u setup unraid? So on a Windows PC maybe? don't like the idea of building my server and waiting the best part of a week for the preclear to be done :(. Thanks spaceinvader

[@SpaceinvaderOne]

Not in windows. But what you could do using any computer is 1. download the unraid trial on a USB stick. 2. disconnect the windows hard drives (to avoid accidentally erasing them) 3. connect your new hard drives either by SATA or a USB adaptor 4. boot computer from USB (then you will have unRAID up temporarily on that PC) 5 preclear your disks :)

[@hamzaafandi9293]

Spaceinvader One amazing advice thank you. this is exactly what I'll be doing. I have many drives to use and the last thing I wanted to do was wait for a week before playing with unraid. I'll do what you said. Thank you :)

[@ProjectR86]

Great video as usual, couple of quick questions though: can I preclear multiple drives simultaneously? If yes, would it impact performance? Can I preclear on a different computer then bring the drives over to the server? (I assume this is fine) I'll be setting up a new array with new drives all in one go and would like to save some time if I can do it simultaneously.

[@SpaceinvaderOne]

Hi Project.R, Yes you can preclear more than one drive at once. When i preclear a couple of drives at once i normally keep them outside of the case as preclearing takes a while and the drives can get hot. But shouldnt effect the performance.

[@ProjectR86]

Alright, thanks for the reply.

[@VanFS3K]

I would like to see the Race Frame Project please

[@SpaceinvaderOne]

very soon :)

[@VanFS3K]

Preclear died when Unraid 6.4.1 came out

[@MortenBN1988]

As in it doesn't work anymore? Or is it built in now?

[@VanFS3K]

Its no longer supported and Unraid recommends you do not install it. Apparently the built-in functionality works similarly, which makes Preclear not as relevant as it use to be

[@MortenBN1988]

Okay, thanks for the quick reply. I'm waiting on hardware for my first Unraid setup to arrive so i'm trying to learn everything i can while i wait. :)

[@michaeltuttle1106]

Discussion about why it's unnecessary lime-technology.com/forums/topic/54648-preclear-plugin/?page=74&tab=comments#comment-638898

[@methanoid]

Ed, I was just about to preclear 8 x 10Tb drives on a 2nd server and found that PreClear Plugin is deprecated in 6.4.1 onwards... Might be worth flagging?! lime-technology.com/forums/topic/54648-preclear-plugin/?do=findComment&comment=638898

[@lazerusmfh]

I have 8 12 Tb disks in my home array, I’ll take my chances and not preclear holy shiz it would take forever

[@bquincygriffin]

Good content. The music really ruins the otherwise great video. Super irritating!