Hi Bigfoot,Now that you have dedicated a lot of time, I would recommend you do a backup with Clonezilla or some bare metal backup software. At least then if you have problems, it will take 15-20 minutes to do a restore on a new drive.
I do periodic Clonezilla backups (OS only) for my HDA and have restored a few times in the past with no issues. That includes when my drive was going bad and had to be replaced. Clonezilla had me back up and running within 30 minutes of installing the new drive.
In the case that you have setup Greyhole to have double copies of everything on both drives...then yes...replacing a drive will take only 15-120 minutes, just for the OS.
In my case I have a 1 TB and 750GB drive together in the storagepool and only Pictures-share is set to have double copies.
And at the time of replacing the failing drive I had to copy close to 750GB of data...I dont think that is possible in 15-20 minutes.
Also dont forget...the drive had bad sectors and unreadable sectors (that were pending)...you either loose data of you just skip those, or it takes a long time if you want to be safe and copy as much as you can rescue.
I am glad I have the HDA up and running again. In the end the procedure was easy and resulted in a perfectly copied main drive loosing under 700kb in 33 errors.
I dont think there is a way to copy data from a damaged/failing drive any quicker without loosing data.