Technology considerations in selecting a direct attached storage solution for HP ProLiant Gen8 servers

Introduction

HP ProLiant Gen8 servers embody more than 150 design innovations. By engineering ProLiant Gen8

servers for enhanced solid state performance and by adding intelligent algorithms and analytics to

manage performance, resiliency, and data protection in real-time, we made ProLiant Gen8 servers an

all-in-one platform optimized for your storage workload demands.

The direct attached storage (DAS) solution you choose for your systems affects their performance,

cost, and usability. To find the best solution for your environment, you should take into consideration

interconnect technology, controller technology and features, as well as drive types and configurations.

This technology brief discusses all these considerations for direct attached storage to HP ProLiant

Gen8 servers. Note that we include multiple types of DAS:

• Storage that connects directly to the drive controller or through an expander to the drive controller

• Storage within the server chassis or in an external chassis

Interconnect technology

Technologies to directly attach one or more drives to a computer system include Serial ATA (SATA)

and Serial Attached SCSI (SAS). SATA and SAS have replaced parallel SCSI because of their higher

throughput, simpler cabling, and support for more drives per port. Each drive with a SATA or SAS

interface has its own high-speed serialized communication channel to the controller or expander.

Serial ATA

SATA uses a point-to-point, half-duplex, serial connection and the ATA command set. This command

set is simpler but provides less robust functionality than the SCSI interface used with SAS. The SATA

interface now has performance enhancements such as native command queuing (NCQ) and speed

increases up to 6 Gb/s. SATA is the best solution for price-sensitive, low I/O workload applications.

Serial Attached SCSI

SAS uses a point-to-point, full duplex, serial connection and the SCSI command set. This command set

provides better performance than SATA. Also the SCSI error handling protocol, which is superior to

SATA, increases SAS reliability. SAS devices can have dual ports for link redundancy and can access

the full bandwidth of a SAS link. SAS is the best solution for highest performance, high I/O workload,

and mission-critical applications.

Interoperability

SAS shares physical characteristics with SATA. SATA drives can connect to SAS controllers operating

at the SATA link speed and through expanders using SATA Tunneling Protocol (STP). You can use

SATA and SAS drives in a single enclosure to meet capacity, performance, and cost goals; but you

cannot mix them in the same logical array. In addition, you cannot use SAS devices with SATA

controllers.

Expanders

SAS expanders allow one SAS port to connect to multiple drives or other expanders. HP SAS

Expander Cards and ProLiant Gen8 Expander Backplanes allow servers to connect more drives per

port, use more than eight internal drives in a RAID array, and spread a RAID array across multiple

drive cages.