I currently have only one free slot and would soon like to use it for data. Can I preclear a couple of drives and put them aside? If I take a precleared drive out of the server does it lose the signature? Or can I keep a stack of cold precleared drives ready as needed?

I believe I asked this question a while back and the answer was yes.  Thats what I do.  I have 2 drives i've precleared that are waiting to be used to swap with bad drives as needed.

Losing the preclear signature will only happen if something writes to the drive. BTW, replacing a failed drive does not use the preclear signature for anything, the only reason it helps is when adding a new drive to an already protected array. I would still use preclear just for the extensive drive testing it does, but the signature is a moot point if you are rebuilding a failed drive.

replacing a failed drive does not use the preclear signature for anything

Ah, OK, I thought unraid zeros a drive before rebuilding to it. I thought preclearing it would save that extra time.

I currently have only one free slot and would soon like to use it for data. Can I preclear a couple of drives and put them aside? If I take a precleared drive out of the server does it lose the signature? Or can I keep a stack of cold precleared drives ready as needed?

When you say "slot" do you mean drive bay or SATA port? My case is full but I have free ports so I just use an eSATA enclosure for preclears.

As noted, you can pre-clear as many drives as you want;  but they won't save any time at all if you're replacing a drive for a rebuild.    It WILL let you add another drive (in your available slot) very quickly whenever you decide to do that, however => and it's also a very good test of a new drive to ensure it's good before you put it to use in UnRAID.

 

But realistically, if you pre-cleared two drives ... one for the soon-to-be-used additional drive, and one as a well-tested spare ... that's all you reasonably need. 

On the other hand, if you keep more than one spare there is a good chance that by the time you use up the first one and need another, the prices will have dropped and the capacity will have increased, so you will have bought a smaller drive than you could have and at a higher price.

Agree -- that's why I suggested there's no need for more than one spare.    I used to take advantage of many sales that "seemed" like great prices to grab a few extra drives ... but haven't done that for years, as I'd end up with new, unused, drives that I had no desire to use anymore because of the higher capacities I could get when I needed more storage 

 

I now have one spare 2TB and one spare 3TB for my two UnRAID arrays -- and that's it.  Even those probably won't get used if I need a new drive -- I'll likely pop in a 4TB drive when needed 

 

[but at least the spare 2 & 3 TB drives will serve well as backups -- I DO maintain a complete backup of all of my data, so I need an extra drive or two each year for that]