What's the difference between a SAS disk and a SATA disk?

Many people mention the SAS disk and SATA disk, the first thought is the difference between the interface, the SAS interface speed is much higher than SATA, so that the SAS disk than SATA disk faster, high performance. In fact, the interface is not the difference between the main, but only a small aspect. So where is the biggest difference between SAS disk and SATA?

This is an internal analysis of the disk, the most important for a disk is the drive motor (actuator), the head (Read/write heads) and the disk surface (discs). SAS disk is an enterprise application disk, we can call it Enterprise Disk,sata disk is for ordinary users, for performance, reliability requirements are not high applications, we can also call Nearline disk. The most important requirement for SAS disk is high data throughput, low latency and high reliability. In order to achieve this demand, the SAS disk's internal drive motor performance will be relatively high, speed will be relatively fast. However, a fast speed can cause additional problems. For example, high disk internal temperatures can affect the stability and reliability of data reads. Therefore, in order to achieve a very high speed, but also to ensure the reliability of the system, the SAS disk has added a lot of sensors to the temperature of closed-loop monitoring, so that the temperature of the system to achieve a constant, not too high. In addition, the disc substrate inside the SAS disk also needs to be specially designed, and the base inside the SATA disk is completely different. As shown in the following illustration, the SATA disk is made of aluminum substrate, and the SAS disk is based on a glass material base plate. The advantage of using aluminum material is high storage density, however, the overall flatness of the substrate is not high, which brings serious reliability problems. In the microscopic world, the uneven substrate is like the hilly area, when the head is running at high speed, if there is a trouble, the head will collide with these hills, resulting in disc disc scratches, data loss. The advantage of the glass substrate is that the flatness is high, but the storage density is not as high as the aluminum material, which results in the data storage capacity of the SAS disk is less than the capacity of the SATA disk.

Obviously, in many design decisions, SAS gives priority to reliability, while Sata considers cheapness and large capacity. Because of the performance of the SAS disk in terms of throughput and latency, the common IDE and SATA interfaces are unable to meet the requirements of the application, and therefore require support from other high-performance interfaces. The interface technologies that typically support SAS disks are FC, SCSI, and SAS, and support dual ports, which are designed to meet the needs of enterprise-class high-reliability applications. In terms of data transfer protocols, SAS also need to consider software reliability, so the ATA protocol for SATA disks is clearly not enough, so a SCSI data transfer Protocol is used for this high-performance disk.

Through simple analysis, we can understand that the SAS disk and SATA disk is not only an interface problem, the internal deep reason is the SAS disk to meet High-performance, high-reliability applications, SATA disk to meet the large capacity, non-critical business applications.

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