Adaptec RAID 5 degraded but all HDD are reported as optimal

Although kind of late:

You have a Raid 5EE with 1.819 TB. To reach that size with those harddisk sizes you need 6 HDDs with 465GB (n-2) and you cannot think of the Hotspare as a Hotspare like in Raid 5. The Hotspare is used in the array to enhance the performance. So in Raid 5EE when one drive fails the array is essentially degraded until it has finished compression, where it starts relocating data to the reserved space on the intact drives. If you loose another drive while the array is being compressed the array fails instantly as it is not possible to finish compression. That's the only way how you can have a Raid 5EE with 2 drives missing and the array being failed instead of just degraded.

Of couse, sadly this means your data is gone if you don't have another backup.

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".