SAS Drive Explained

SAS stands for Serial Attached SCSI (SCSI Stands for Small Computer System Interface, typically pronounced as “scuzzy”) and is a technology for transferring data from and to hard drives.

Whilst SAS refers to the interface it is typically used to describe a type of hard drive, usually 10K or 15K SAS.

The higher speeds and a higher level of resilience make SAS the obvious choice for Enterprise use and in situations where high speed and reliability are paramount.

SAS hard drives come in 2 main types: 10K and 15K. The K refers to the rotational speed of the hard drive, i.e. 10,000 and 15,000 revolutions per minute respectively.

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SAS Speeds

In terms of speed the best measure is IOPS (Inputs Outputs Per Second) which measures the data throughput which defines the rate at which data can be read from or written to the hard drive.

A typical 10K SAS drive operates at around 120 IOPS and 180 IOPS for a 15K SAS Hard Drive. . This compares to around 80 IOPS for a 7.2K SATA Hard Drive. Solid State Drives can operate at a range between 4,600 to 75,000 IOPS depending on the type of SSD.

SAS Capacity

SAS disks can range from 300GB to up to 900GB. They are lower capacity than SATA drives but what they lack in capacity they make up for in terms of speed and reliability.

SAS Reliability

SAS hard drives are intended for use for high demanding applications where speed and high availability are the primary concerns.

SAS drives have a Mean Time Between Failure (MTBF) that is generally accepted to be around 1.2 million hours. This compares to around 700,000 hours for SATA drives and approximately 2 million hours for SSD drives.

SAS Power Consumption

SAS drives typically consume between 5 to 7 Watts when idle and between 10 to 14 Watts in normal operating conditions.

Advantages of SAS over SATA

SAS has several advantages of SATA based drives.

SAS drives are faster and have more bandwidth throughput than SATA drives. SAS drives are also more reliable than SATA.

For these reasons, ultimately SAS tends to be used for Enterprise applications use whereas SATA is aimed at the consumer market.

However, speed and reliability come at a cost and SAS drives do not have the capacity that SATA drives offer and tend to be more expensive per GB.

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