It would be VERY interesting to understand the rational behind this compatibility chart.
Not so surprisingly, the “cheap” drives are recommended for the “cheap” Drobos (Drobo, Drobo-S, Drobo-FS).
But such a recommendation should be based on technical compatibility, not market acceptability.
And it is VERY difficult for me to reverse engineer the rational for this table :
[list] for years, Drobo Inc. has pretended that the lack of TLER (Time Limited Error Recovery) was not an issue on Drobo “because it is not a RAID”. But they never justified such an assertion, which is hard to believe when you understand what TLER is and why its lack can be problematic when a second layer of error detection/correction is imposed on top of a disk set
 similarly, hard to understand why the Load Cycle Count (aka LCC) should be an issue on some Drobos but not all, when all of them are running similar flavors of Linux
[*] longevity, supposed to be better for “professional” drives, should not be a compatibility issue at all, since the whole purpose of the Drobo is to overcome the disastrous consequences of a disk failure[/list]
At that point, I would be sorely tempted to assume that this “compatibility chart” is more marketing bull…t, the split being :
[list] on cheap Drobos one pretends to ignore the consequences of some missing disks features (because prosumers can afford more easily to lose data ?; or are supposed to be more gullible ??), since the added cost of “professional drives” would price the Drobo out of the market
 on more expensive ones, where “cost is not an issue”, the need for such disks features finally emerges…
[*] or alternatively, there is no more need for (some ? all of ?) those disk features on high end Drobos, but recommending them gives Drobo Inc. more credibility when selling to professionals used to “the more expensive, the better”[/list]
If Drobo Inc. was more transparent about the detailed technical criteria for a “fully compatible Drobo disk”, that would also allow Drobo users to investigate utilities which may allow activation of “professional features” on lower prices disks (TLER, LCC, …) since most of those are perfectly able to support them, they are just inhibited by default by the manufacturers to force “rich professionals” to buy the more expensive ones