(in the bios that is) …
I was madly making RAID arrays the other day to do some testing, when a message popped up on the screen … “The selected configuration allows for the creation of a logical device with Enclosure Level Redundancy. This will override any second-level devices selection that you have made. Do you want to configure Enclosure Level Redundancy? Y/N”
Now I have a bad habit of just ignoring pop-ups (which causes me some pain occasionally), but this one had me intrigued. Either I was asleep during some training session (not uncommon) or someone left me out of the loop.
So what does this mean (the message, not the sleeping bit). I said yes and nothing exciting happened (very disappointing). That really got me intrigued so I looked at the properties of the array I had created.
My old Supermicro 815TQ is an 8-drive 2U system. Even though it looks like one backplane it’s actually considered by Supermicro (and our cards) as two backplanes … a row of 4 drives above a row of 4 drives in separate backplanes. Since I was making RAID 10s using all 8 drives, the card saw something I had not considered (and did not have control of anyway) … that it could make each pair of mirrors in my RAID 10 with one drive on each backplane for each mirror.
Simply put, if one backplane fell over, the system would keep running. The card is smart enough to see an opportunity to add an extra level of security, simply because of the configuration of my system and the raid level I was using. Cool!
The morals to the story are many … read pop-ups, stay awake during engineering briefings and when prompted to do “enclosure level redundancy” … do it.