With Comcast pausing data caps I've been downloading an awful lot of stuff the last month and my Drobo filled up. I offloaded data to some spare old hard hard drives but I think it's time to upgrade my Drobo internal hard drives.

Currently it's: 2 x 4 TB + 6 TB + 2 x 8 TB for 20 TB usable storage (with the rest going to RAID redundancy).

I was thinking of getting 5 x 18 TB to max out the 64 TB usable storage (64 TB due to that's how much Drobo OS can handle). But their latest support doc (Aug 2017) says that 14 TB hard drives are the largest tested.

And actually I may have been computing this wrong. If we look at the capacity calculator, 5 x 14 TB = 70 TB but about 63.66 TB raw capacity. So if the Drobo RAID stuff is done in one volume by the OS then this is the max and the 50.84 TB useful storage is also the max.

Once that is decided, looking at their drive selector page they have four options:

Seagate Barracuda Pro (14 TB, Desktop, $440)
Seagate Ironwolf Pro (14 TB, NAS, $480)
WD Red (14 TB, NAS, $500)
WD Red Pro (14 TB, NAS, $570)

WD Red is what I use. They're 5400 rpm and write speed is not great. I think I want 7200 rpm drives. With the recent reveal that Western Digital slips SMR drives into WD Red channel I guess I'll try Seagate Ironwolf Pro. CMR drives are traditional while SMR drives are cheaper but require read/writes to be serialized as much as possible (i.e. if you have multiple threads doing read/write it's going to be much slower than CMR). This requires a special driver.

I'll probably buy a set next month from B & H.