Hi Brain's Trust - just want to understand the best procedure on how to replace an old 2TB WD Caviar drive with a recently purchase 6TB WD Red drive.

My Parity is 6TB and my Disk7 which is nearly 15 years old has just shown its first Smart error so I feel its time to replace it. I've just bought a new 6TB drive and haven't pre cleared it yet but I wanted to understand the best procedure to replace the drive. I thought that I couldn't replace a 2TB with a 6TB but perhaps nowadays you can easily with parity rebuild so wanted to test this theory here.

I have backed up all the data on my 2TB drive so if the drive fails it's no loss as I have the data backed up but I am just checking to see if the procedure it to remove the drive, where Unraid will determine the drive is missing, replace it with the 6TB drive where it will then try to rebuild that drive with the contents of the old drive and given my Parity is 6TB it will rebuild that drive. My questions are: will this procedure work and secondly, will it preclear is this drive before rebuilding it or should I plug the drive in via USB and SATA external connector to firstly preclear the drive before doing the drive swap and rebuild as I don't have spare slots in the Unraid NAS tower.

Current configuration is as per the following: Disk7 is to be replaced with a WDC 6TB drive that is yet to be precleared - brand new in its box.

Welcome expert's thought on this before I proceed!

Thanks in advance guys,

Cheers,

Mike.

You just need to power down, connect the new disk, assign it and start the array. More details here:

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/array-configuration/#replacing-disks

Thanks JorgeB - can I assign the new drive without having pre-cleared it (i.e. should I connect this drive via USB and SATA connector to my array and pre-clear it first before removing my incumbent drive from the array, then adding this new larger un-precleared drive) - or can I just add it and Unraid will do the rest - i.e. preclear it and then rebuild the 2TB worth of data from my old disk and having 4TB of free space? I don't have a spare slot in my NAS array, so would need to connect the new disk with a USB and SATA connector to pre clear it.

Also - thanks for the quick reply! Much appreciated.

Cheers,

Mike.

7 minutes ago, MikeyJeff said:

can I assign the new drive without having pre-cleared it

Yes, preclear is always optional.

Prec

7 minutes ago, MikeyJeff said:

can I assign the new drive without having pre-cleared it

Existing contents are irrelevant. A Preclear is unnecessary (unless you want to first stress test the drive) as the rebuild process overwrites every sector on the drive so any Preclear gets overwritten anyway.

Okay understood. If I did want to pre clear is there any issue with connecting via USB and SATA adaptor and performing that process before connecting the drive and unraid doing a rebuild from parity or is it really surplus to requirement and not necessary.

Thanks for the insight guys!

Mike.

Edited September 26, 2025Sep 26 by MikeyJeff

46 minutes ago, MikeyJeff said:

Okay understood. If I did want to pre clear is there any issue with connecting via USB and SATA adaptor and performing that process before connecting the drive and unraid doing a rebuild from parity or is it really surplus to requirement and not necessary.

Thanks for the insight guys!

Mike.

You can connect via USB for the Preclear. However doing so will make no difference to the rebuild which ignores the Preclear so the only purpose would be to stress test the drive before using it in the Unraid array.