Drive Form Factors
For AdvancedTCA (ATCA) in-shelf storage, the lower profile 2.5-in. drives are the most popular since they can be mounted on ATCA blades or AdvancedMC (AMC) modules with hot swap capability. More traditional 3.5-in. drive form-factors still keep a small lead on capacity and performance over the 2.5-in technology, but are typically used in external storage arrays.
SAS (serial attach SCSI) drives are the benchmark—they are the most reliable and highest performing hard drives available with MTBF figures of more than 1.2 million hours and high spindle speeds of 10,000 and 15,000 RPM. One drawback of SAS drives is a limit on case temperature that often leads to difficulties cooling the drives at the 55°C, NEBS environment. In most cases, SAS drives are fairly expensive when compared to other rotating drive technologies.
SATA (serial ATA) drives offer higher capacity, but are a lower performing, lower cost option to SAS drives. They are not usually considered reliable enough for carrier grade equipment. However, some vendors produce “extended” or “extreme” versions of their SATA drives and in some cases are acceptable for carrier grade equipment. These drives can therefore be used for applications where reliability and cost is important, but performance can be sacrificed.
SSD (solid state drives) are of limited capacity and expensive, but are high performance, reliable, low power, and can work in high ambient temperatures. They are becoming popular when capacity needs are low, or when performance is required and SAS drives cannot be used. As prices fall, this technology will become more and more important.