What would the rebuild time be for a raid6 rebuild using 24x12tb hds?If your are using an expander backplane, you'll only need the one card. Pretty much any HBA would do you, but the LSI based cards are very well tried and tested with these backplanes, so that's what I would stick with. As for which RAID level or how you go about providing redundancy, it really depends on how performant you need the array to be, how risk averse you are etc. If I were looking at using a hardware based raid engine and needing performance, I would be wanting mirrored pairs. If I could live with a disk causing issues and needed some capacity, I would go with double parity raid, so something like RAID 6. I would not recommend RAID 5 now for anything beyond a quick temporary space to stick stuff in transit to permanent storage. However, I see little benefit these days in using hardware based RAID in anything but the most stringent of circumstances. Software based redundancy solutions really are up there with the best RAID cards now, and there are plenty of solutions to choose from. Modern CPU's can easily handle the XOR calcs of even the largest array, without even breaking a sweat, plus you have the added benefit of not being tied to any particular card should that fail at some point. For me, it's a "no brainer"
I would be personally looking at using ZFS and creating either 4 pools of 6 disks each or 3 pools of 8 disks each in RADZ2. I need and want a bit of capacity, but I also want to have that little bit of a safety net as well. This gives me time to correct issues, before I have to consider taking the arrays down. If a disk fails, it can simply be replaced and the array can still be active in degraded mode until a re-silver is completed.
If I needed to bring down the time that it takes to do that, or needed more performance, mirrored pairs would be the way to go, but the way I look at it is that I can have 2 disks fail and still be running, but common sense says replace any disk that fails immediately.
Backups! Backups! Backups! THERE IS NO RAID solution that will save you in a catastrophic failure, so make regular backups and do what nobody else ever does, test them dammit
A pci-e 3.0 x8 slot can do ~8GB/s.Apparently using RAID 5/6 for disks over 4TB is very bad so I'm told. I think it would be bad for 12TB disks. Anyone have thoughts on this?