In short, we are running out of things to tweak as discussed in (see Green_Storage_--_Do_Disk_Drives_Matter?_Yes,_but_....).
For enterprise-class drives, there are simply fewer degrees of freedom because we are reaching the limits of air cooling and recording surface area. Historically, developers could vary:
- Areal Density,
- Platter Diameter,
- Rotational Speed (RPM),
- Number of platters,
- Seek Times/ Actuator Speed.
In the past, all of these contributed to a steady progression of smaller and smaller drives still providing equal or better capacity and performance. However, this progression is near its end because:
- Areal densities are becoming harder to increase.
- Smaller platters such as those in 2.5" drives have too little surface area to meet market demand for high capacities.
- Drive vendors can add platters to achieve the required capacities, but the 1U server vendors can’t cool them. And this is the bulk of the market.
- Rotational speeds over 15,000 RPM generate too much heat.
- Faster seek times need too much heat, or the mechanical parts are too big.
Nonetheless, the industry is shifting to 2.5" drives for tier 1 storage, although to meet capacity demands, suppliers will require more spindles than with 3.5" drives. Moreover, 2.5" is likely to be the last in the progression of form factor reductions, as semiconductor technologies encroach on lower capacity ranges. Perhaps the disk array vendors will convince the drive vendors to produce 2.5" devices with more platters and therefore more capacity, but this will take two to three years to play out, and the drives will carry a premium cost.
Note that the market for slower 3.5" SATA drives will remain robust for non-tier 1 applications, perhaps extending the life of this form factor.
Action Item: For those who are desperate – out of power or cooling - the best strategy is to deploy lower RPM drives and look to water cooling if possible.
For those who are not desperate, the best strategy is to wait for the vendors to commit to their green storage strategies while addressing the organizational issues discussed in Can_IT_be_cool_again?.