Serial attached SCSI or serial ATA hard disk drives: how to choose one or the other--or both. (Tape/Disk/Optical Storage).In looking at future storage industry needs for enterprise or desktop, which hard-disk drive is the best investment for a specific application? How can the end user save money and still have the reliability and performance required for the task? To answer these questions, a performance, feature and cost comparison between Serial Attached SCSI See SAS. (SAS (1) (SAS Institute Inc., Cary, NC, www.sas.com) A software company that specializes in data warehousing and decision support software based on the SAS System. Founded in 1976, SAS is one of the world's largest privately held software companies. See SAS System. ) and Serial ATA See SATA. Serial ATA - Serial Advanced Technology Attachment (SATA (Serial ATA) A serial version of the ATA (IDE) interface, which has been the de facto standard hard disk interface for desktop PCs for more than two decades. The original Parallel ATA (PATA) interface was launched in 1986. ) hard disk drives and the considerations in choosing the optimal hard disk drive for a particular application, must be addressed. End users are looking for Looking for In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with. ways to save money on the purchase of storage equipment and performance, capacity, reliability and scalability have to be factored into any purchase decision. Overriding future storage needs are performance and capacity, as increasingly vast amounts of data and the long distance transmission of data become the norm. With current data rates at 1.5- to 2.0Gb/s and increasing to 6.0Gb/s in the foreseeable future, performance is high on the requirements chart and cost containment cost containment, n the features of a dental benefits program or of the administration of the program designed to reduce or eliminate certain charges to the plan. is not far below. An exciting new feature for optimized, affordable storage is combining SAS and SATA drives in a single SAS system (1) Originally called the "Statistical Analysis System," it is an integrated set of data management and decision support tools from SAS that runs on platforms from PCs to mainframes. . Each technology brings its unique innovations and functionality to the storage application as their specifications and connectivity are being made compatible due to the efforts of the SCSI Trade Association The SCSI Trade Association, or SCSITA, is an industry trade group which exists to promote the use SCSI technology. It was formed in 1996 [1]. As of 2006, major members include Adaptec, HP, Intel, LSI Logic, Seagate, and IBM [1]. and the SATA II See SATA. Working Group. To better understand the contributions made by each technology, both are explained more fully. What is Serial Attached SCSI? Serial Attached SCSI (SAS) carries SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. forward to new generations of storage 110. It builds on 20-plus years of reliable SCSI technology with many enhancements added over the years. Its quality, reliability and universal compatibility will more than meet the requirements of the future enterprise storage market. Due to its SCSI forbearers, it will benefit storage management, reduce the risk of storage technology change and increase system interoperability, flexibility and scalability. SAS is point-to-point technology with expander architecture. This combination offers high performance and reliable solutions that are quickly and easily deployable in the market. Beginning in 2004, when SAS products enter the market, its effect on the enterprise storage industry is expected to be significant. What is Serial ATA? Serial ATA (SATA) has a solid, reliable position in the desktop industry going back to 2001 when SATA 1.0 specification was completed with a performance rate of 1.5Gb/s. Its heritage is ATA (1) (AT Attachment) The specification for IDE drives. See IDE. (2) See analog telephone adapter. ATA - Advanced Technology Attachment , which is firmly grounded in the internal desktop storage industry. SATA is positioned to go into the future as the serial successor to ATA, continuing on the desktop, entry-level server and entry-level networked storage systems. As a serial 110 technology, SATA is a point-to-point topology topology, branch of mathematics, formerly known as analysis situs, that studies patterns of geometric figures involving position and relative position without regard to size. . It enables hot-plug devices, thinner and longer cables and cyclical redundancy checking See CRC. (CRC (Cyclical Redundancy Checking) An error checking technique used to ensure the accuracy of transmitting digital data. The transmitted messages are divided into predetermined lengths which, used as dividends, are divided by a fixed divisor. ) for enhanced data reliability. SATA is currently gaining enhancements from the specification called "Extensions to Serial ATA 1.0." Definition of system-level device activity SATA command queuing The ability to store multiple commands and execute them one at a time. , extended differential voltage ranges and LED behavior are included in the extensions. SAS and SATA Feature Comparisons The SAS feature advantage is in data security, integrity, reliability and availability in support of enterprise mission-critical applications that must be online and running 52 weeks a year. These are online transaction applications where data availability Refers to the degree to which data can be instantly accessed. The term is mostly associated with service levels that are set up either by the internal IT organization or that may be guaranteed by a third party datacenter or storage provider. must be constant around the clock with no data lost. SAS is full-duplex and dual-ported to SATA's half-duplex and single-port capability. SAS contains expander architecture and activity indicators. SAS will be able to scale to around 200 devices and SATA by one device. The emerging SATA II Port Multiplier Also called a "fan-out," it is a device that expands one port into several. For example, an Ethernet port multiplier allows multiple stations to be connected to a 10Base5 cable via one transceiver tap. Otherwise, each station requires its own transceiver. specification allows up to 16 SATA devices to be connected to a single SATA host port. SAS system architecture is being designed to support SATA protocol so that the system controller readily recognizes SATA drives along with SAS drives. SATA responds to a single initiator, while SCSI responds to multi-initiators. SAS and SATA drives can reside side by side in the same enclosure and the system controller talks to each in its own language and coordinates their activities and performance. This gives the user a high level of flexibility in configuring a storage system to provide exactly what the application requires- at the least cost. Summary As SATA drives become faster and gain more features, they will be suitable for entry- level enterprise applications. The advantage of SAS and SATA drives in the same system is that they will be able to operate side by side on a SAS backplane An interconnecting device that has sockets for printed circuit boards to plug into. Passive and Active Although resistors may be used, a "passive" backplane adds no processing in the circuit. in support of more than one application. Depending on the immediate need, either the SATA drives or the SAS drives, or both, can be selected by the system. The outcome is that the total cost of the system will be less, reducing the total cost of ownership (TCO (1) (Total Cost of Ownership) The cost of using a computer. It includes the cost of the hardware, software and upgrades as well as the cost of the inhouse staff and/or consultants that provide training and technical support. See ROI. ) and increasing the return on investment (ROI (Return On Investment) The monetary benefits derived from having spent money on developing or revising a system. In the IT world, there are more ways to compute ROI than Carter has liver pills (and for those of you who never heard of that expression, it means a lot). ). In considering the best choice of disk drive for enterprise or desktop applications between Serial Attached SCSI and Serial ATA, performance, cost, capacity, integrity, scalability and flexibility all have to be factored into a purchase decision. For the desktop and laptop markets, SATA drives are preferred because they are lower in cost and have the features and benefits that support desktop applications. For transaction processing Updating the appropriate database records as soon as a transaction (order, payment, etc.) is entered into the computer. It may also imply that confirmations are sent at the same time. Transaction processing systems are the backbone of an organization because they update constantly. in the enterprise requiring a high level of performance and data integrity, SAS is the preferred choice. Where entry-level enterprise applications are concerned, the decision process is more complex since both types of drives can be used, either singly or in combination.
Figure 1
SAS and SATA Disk Drive Comparison
Summary of Drive Differences
Drive Comparison Table Desktop S-ATA
Performance (Access to Data)
Latency + Seek Time 13msec @ 7200rpm
Command Queuing and Reordering LBA based
Rotational Vibration Tolerance 5 to 12 rads/sec/sec
Typical I/Os per sec/drive (no 77
(RV)
Typ I/Os per sec/drive (10 35
rad/sec (2))
Typ I/Os per sec/drive (20 < 7
rad/sec (2))
Duplex Operation Half
Customization
Unique Code and Hardware Limited
Variable Sector Sizes No
Mode Page Parameter Control No
Inquiry Data No
Diagnostic Pages No
Capacity Controls No
Indicators
Activity LED No
Fault LED No
Reliability
MTBF 600K Hrs
Duty Cycle 8 X 5
Interactive Error Management No
Internal Data Integrity Checks No
Dual Port No
Drive Comparison Table Enterprise SCSI
Performance (Access to Data)
Latency + Seek Time 5.7msec @ 15K rpm
Command Queuing and Reordering LBA (1) and RPS (2) based
Rotational Vibration Tolerance 21 rads/sec/sec
Typical I/Os per sec/drive (no 319 (3)
(RV)
Typ I/Os per sec/drive (10 319 (3)
rad/sec (2))
Typ I/Os per sec/drive (20 310 (3)
rad/sec (2))
Duplex Operation Full
Customization
Unique Code and Hardware Extensive
Variable Sector Sizes Yes
Mode Page Parameter Control Yes
Inquiry Data Yes
Diagnostic Pages Yes
Capacity Controls Yes
Indicators
Activity LED Yes
Fault LED Yes
Reliability
MTBF 1.2M Hrs
Duty Cycle 24 X 7
Interactive Error Management Yes
Internal Data Integrity Checks IOEDC (4)
Dual Port Yes
Drive Comparison Table
Performance (Access to Data)
Latency + Seek Time Performance
Command Queuing and Reordering
Rotational Vibration Tolerance
Typical I/Os per sec/drive (no
(RV)
Typ I/Os per sec/drive (10
rad/sec (2))
Typ I/Os per sec/drive (20 Rotational Vib
rad/sec (2))
Duplex Operation
Customization
Unique Code and Hardware
Variable Sector Sizes Var. Sect. Size
Mode Page Parameter Control
Inquiry Data
Diagnostic Pages
Capacity Controls
Indicators
Activity LED
Fault LED Indicators
Reliability
MTBF Reliability
Duty Cycle
Interactive Error Management
Internal Data Integrity Checks Data Integrity
Dual Port
(1) Logical Block Address
(2) Rotational Position Sensing
(3) Queue = 16
(4) Input Output Error Detection Code
The SCSI Trade Association is based in San Francisco San Francisco (săn frănsĭs`kō), city (1990 pop. 723,959), coextensive with San Francisco co., W Calif., on the tip of a peninsula between the Pacific Ocean and San Francisco Bay, which are connected by the strait known as the Golden , Calif. www.scsita.org |
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