How long does it take to rebuild a drive in a RAID 6

I have an Adaptec 5405Z with 20x2TB 7200 RPM drives on a SAS Backplane. I attempted to do a reconfig on it to go from 8 drives to 20 drives. We use it for Security Video Storage. Since the box was essentially brand new, I figured why not see how long it woudl take with ~2TB of data on the array. After about a week and it only getting to 10%, I gave up. Backed it up, wiped it and started over. I tried the same test with RAID 10 and RAID 5, both seemed to crawl, but would have eventually finished. Though in truth, I am certain my DVR software was slowing down the reconfig by constantly writing to the disk. Did you factor additional load on the drives into the rebuild?

Obviously I have a few more drives than you, but for whatever reason, the reconfig seems to drag on for quite some time. When I tried to get Adaptec to answer the question, they weren't much help as the answer seemed to be "it depends on your configuration and how much data is on the array".

I hate to say "don't use SATA" in critical production environments, but I've seen this situation quite often. SATA drives are not generally meant for the duty cycle you describe, although you did spec drives specifically rated for 24x7 operation in your setup. My experience has been that SATA drives can fail in unpredictable ways, often times affecting the entire storage array, even when using RAID 1+0, as you've done. Sometimes the drives fail in a manner that can stall the entire bus. One thing to note is whether you're using SAS expanders in your setup. That can make a difference in how the remaining disks are impacted by a drive failure.

But it may have made more sense to go with midline/nearline (7200 RPM) SAS drives versus SATA. There's a small price premium over SATA, but the drives will operate/fail more predictably. The error-correction and reporting in the SAS interface/protocol is more robust than the SATA set. So even with drives whose mechanics are the same, the SAS protocol difference may have prevented the pain you experienced during your drive failure.