It won’t, that’s how Thin Provisioning works. But there’s some smart mechanism built into the Drobo. As it will be nearing its full (real) capacity, it’ll gradually get slower and slower to write data, up to the point of being barely usable. That, on top of the lightshow on the front Drobo panel and the alert messages from the Dashboard, of course.
i wonder if there is a way that drobo can implement a Smarter type of thin provisioning in future?
eg, broadcast the real space available, and then when a drive is upgraded, start broadcasting a higher (real) space availability?
its very simply in concept, so i wonder why it isnt done?
Because that’s not simple at all. The hard drive doesn’t “broadcast” anything to the operating system - it’s a block device providing “Read sector xxxxx” and “Write sector xxxxx” functions. The OS reads and interprets the appropriate file system structures and you cannot alter these willy-nilly as you go as they are crucial to data integrity. The only thing Drobo “lies” to the host about is the physical coverage of the “virtual” sectors. There was a “Capacity filter” (or whatever it was called) application long time ago, now apparently abandoned. But it relied on purely software solution with Dashboard “injecting” the free volume size into the special kind of driver thing - not by Drobo “lying” to the host OS.
To clarify: of course Drobo answers to the maximum available (virtual, it that case) blocks query, but changing it on the fly wouldn’t change anything regarding the already established volumes. Just like performing a raw volume copy to larger drive wouldn’t magically expand this volume.