SAS vs SATA SSDs. What to choose?

    Good afternoon habralyudi!

    HGST's blog is back with you after a break. And today we would like to talk about the advantages of SAS SSDs over SATA drives.

    The SAS interface, which supports communication between devices, is designed for enterprise use and provides scalability, reliability and high data availability, while SATA devices are optimized for cheaper user applications.

    Since disk manufacturers use the SAS interface for high-performance drives and the SATA interface for client drives and mass storage devices, solid-state drive (SSD) manufacturers are largely continuing to use the same partitioning. There are also enterprise-class SATA drives with SATA interface on the market that provide high performance. However, using the SAS interface with more error-resistant flash devices, controllers, and firmware, we get an excellent solution for enterprise-level workloads, such as online transaction processing (OLTP), high-performance computing (HPC), and database acceleration data storage organization / data logging, virtualization and virtual PC infrastructure,

    With SAS interface features and industry-leading HGST technologies such as CellCare, PowerSafe, and Data Path Protection, you get the following benefits:

    • Stable, high-performance SSD performance over its entire life cycle
    • Durability
    • Scalability
    • Reliability in use
    • High data availability
    • Data manageability on the device
    • Interaction with a streamlined system architecture

    Workloads that must be supported by enterprise-class solid-state SAS drives include:
    • Online Transaction Processing (OLTP)
    • High Performance Computing (HPC)
    • Database Acceleration
    • Organization of data warehousing and storage of user data
    • Virtualization and infrastructure of virtual PCs
    • Analysis of large volumes of data and hyper-scalable data
    • Messaging and collaboration programs
    • Interface with web servers
    • Streaming multimedia and on-demand video programs (VOD)
    • Cloud computing
    • Tier-0 storage devices for SAN and NAS systems

    SAS (serial SCSI) and SATA (serial ATA) are standard protocols for transferring data between connected devices. They are designed to enable computers to interact with peripheral devices such as external memory controllers and hard drives. Both interfaces (SAS and SATA) have a long history of development: they first appeared in the 1980s as parallel interfaces, and about 10 years ago they were converted to serial protocols in order to further improve performance. When used with an external memory controller, the SAS or SATA interface can be used as an external server interface, as well as an internal interface for connecting hard drives and SSDs. A controller can support many types of interfaces, however, disks have only one type of interface - SAS or SATA. The interface is independent of the information storage device (for example, flash memory, hard disk) or the quality of components or firmware inside the disk. From this point of view, the SAS and SATA interfaces behave identically.

    Let's look now at the basic parameters of drives

    • SCSI protocol. The SCSI protocol used by the SAS interface is faster and performs multiple, simultaneous data I / O operations more efficiently than the ATA parallel interface command set (SATA).
    • Increase in data transfer speed - from 6 Gb / s to 12 Gb / s, and then up to 24 Gb / s. The SAS interface allows you to increase the data transfer rate from 6 Gb / s to 12 Gb / s; In addition, there is a clear roadmap to further increase the speed of up to 24 Gb / s. Currently, the SATA interface supports data transfer rates up to 6 Gb / s, while there are no specific plans to increase the speed in the future.
    • Queues of tagged teams. Most SAS drives support a 128-bit deep command queue (protocol limit of 65,536), which reduces latency and improves performance at high workloads. Hardware setting of the command sequence of the SATA interface supports only 32 commands.
    • Dual ports and multi-channel input-output. Drives with SAS interface are equipped with dual ports and support many initiators in the storage system; thus, multi-channel I / O and load balancing can increase productivity. The SATA interface does not support multiple initiators, and most SATA drives do not have dual ports.
    • Full duplex data transfer. SAS drives support full-duplex mode (simultaneous data transfer in two directions), while SATA drives work in half-duplex mode (data transfer in one direction).

    • You can connect multiple drives to one port. The SAS interface supports a port expander for up to 255 devices (two-tier structure), so up to 65,635 disks can be connected to one initiator port. The SATA interface uses only a point-to-point connection.
    • Use of extended cables. Using SAS devices will provide a more convenient process of expanding the data center (data center), since they allow the use of passive copper cables up to 10 m long and optical cables up to 100 m long. SATA does not allow the use of cables over 2 meters long.
    • Scalable performance. The performance of solid state SAS drives in a RAID configuration is more scalable than SATA drives.
    • Compatible with SATA interface. External memory controllers with SAS interface support SATA drives, which provides tiered data storage using both SAS and SATA drives in a single array. However, in turn, SATA does not support SAS drives.

    High data availability
    • Dual ports for fault tolerance. SAS supports dual ports, while most SATA drives do not.
    • Several initiators. The SAS interface allows the connection of several controllers to a set of hard drives in a data storage system, which ensures their quick replacement and switching to another resource in the event of a failure. The SATA interface does not have such capabilities.
    • Connection in the "hot" mode. SAS and SATA drives can be connected in hot swap mode.

    Interacting with a streamlined system architecture
    • Roadmap for future expansion. The plans of manufacturers of devices with the SAS interface include increasing the data transfer rate up to 24 Gb / s and, probably, even higher, while for SATA there is no such roadmap and the data transfer speed is limited by the current value of 6 Gb / s. Through the use of SAS, enterprises can upgrade their fleet of devices and upgrade to faster drives in the future, while maintaining compatibility with previous versions used in existing infrastructure.
    • SCSI. Because most drives installed in the enterprise use the SCSI instruction set, the SAS interface remains compatible with generations of storage systems.

    HGST SSDs feature high performance over the life of the drive. They use innovative Advanced Flash Management and CellCare technologies, which provide extremely high speed in sequential and random read / write mode. SSDs are much faster compared to hard drives, although flash memory cells wear out and their speed decreases, especially with an increase in the number of program installation / file deletion cycles. HGST's Advanced Flash Management Technology uses a traditional wear leveling algorithm, as well as error detection and correction schemes, damaged unit recovery, and data redundancy elimination to increase the life, reliability and performance of SSDs.

    HGST CellCare is a patented technology for the production of flash memory controllers, which allows for the durability, performance and reliability of enterprise-class devices using cost-effective, high-density logic chips for flash devices. CellCare technology consists in dynamically tracking memory cell parameters as they wear out and using prediction technologies to minimize the wear of NAND flash memory chips by creating adaptive feedback between flash memory and the controller. An equally important aspect of Cellcare technology is the ability to control the aging effect of flash memory and prevent the SSDs from slowing down as their lifespan increases.

    Now, when the cost of data storage has increased significantly due to changes in exchange rates, when choosing the components of the IT infrastructure, you have to show ingenuity and compromise. In our opinion, the repeatedly proven reliability and high performance throughout the entire service life should definitely be taken into account along with other factors. Indeed, in the medium and long term, such a decision will pay off in full.

    In the next post, we will continue the discussion about SSD drives and look at other advantages of HGST in this area.

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