You may think that the legacy vendors have SSD and MAID well in hand. Some do, some don't. While these two technologies are at opposite ends of the performance spectrum, it can be challenging to integrate either of them into a legacy system without compromise. It's not the physical integration that's a problem. SSD, for example, can be purchased in a form factor similar to a disk drive, the objective being to insert that drive into existing drive shelves, giving the supplier easy entry to the SSD market. MAID drives are basically the same as regular drives except with spin-down capabilities. There are concerns with maximizing the investment of either of these technologies when placing them in legacy systems.
The point of SSD is to maximize performance. The I/O capabilities of a shelf full of SSD drives may exceed the I/O bandwidth of the shelf. Several shelves of SSD drives may exceed the I/O capabilities of the storage controllers. This means not getting every ounce of performance possible from an SSD investment. For some implementations that may be OK, but for others that need maximum performance, it may not be. Maximizing SSD performance may require enclosures and controllers dedicated to that task, which may also be a more economical way to deliver SSDs as well. At a minimum, it may require scalable controllers that can match the I/O capabilities of SSD.
The point of MAID is to minimize power utilization by spinning down the drive when it's not being accessed. These drives have to be organized in such a way on the storage systems that they will get a chance to be idle enough to actually spin down. As with SSD, this may require MAID-specific enclosures so the data can be more easily segregated. This also provides the opportunity to make the enclosures more power efficient, since the drive is only part of the power consumed in a storage system.
Finally, SAS could be the single biggest challenge. This interconnect offers high performance at a lower price than the traditional Fibre Channel backend we see in storage systems today. Storage suppliers are going to want to integrate SAS-based drives and interconnects into their current storage systems as soon as they can. Vendors that are starting fresh have the advantage of delivering pure SAS-based solutions, where legacy vendors again have the challenge of retro-fitting them. Some legacy storage vendors have been able to overcome technology integration challenges well. Others are running out of bolts to keep the whole system intact and at some point are going to have to start with a clean slate.