I have two LaCie 5Big Thunderbolt Series Raids, (20TB each) daisy chained and attached to my Mac. They are set Raid0. In Yosemite, they are recognized and work well. I upgraded to El Capitan yesterday and saw that the drives were not showing up in Finder. After searching and not finding any hits about LaCie updates to the drivers, I went back to Yosemite from backup. The drives were there again. This morning, I downloaded the LaCie Raid Monitor software and installed it just in case it might help. I then upgraded to El Capitan again and the drives, again, were not seen in Finder. I reached out to LaCie support to find out if they were aware of the issue and if a new driver was coming out. The person I spoke with informed me that they have not had any other reports. She had me open Disk Utility to see if the drives are seen there. Oddly, 3 of the drives are recognized, the remaining 7 are in an "Untitled" status. She asked if the drives were attached when I did the upgrades, and they were. She speculated that the upgrade process, specifically Spotlight, could have done something that messed with how the OS sees the drives. Her recommendation is to go back to Yosemite, disconnect the drives and do the upgrade again. Once it completes, re-attach the drives and see if they are then recognized. I see some value in that and will do it later today. I wanted to get on this forum, however and see if anyone else has experienced the same or similar with any of their external drives, LaCie brand or not. If so, how have you resolved it? Is there value in contacting Apple about this? I've been approaching this as an issue with the LaCie drives, but is there Apple liability here as well? I'd appreciate any insight on how to resolve this. Again, I can stay at Yosemite and everything will work fine, but I'd like to use El Capitan if there's a way to make this work.