Dell PowerVault MD1000 SAS Solution Manual - Página 5

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A REFERENCE GUIDE FOR OPTIMIZING DELL™ MD1000 SAS SOLUTIONS

The paper presumes that the reader has a basic understanding of different RAID levels and

interconnect technologies – such as Serial Attached SCSI (SAS) and PCI Express. In this paper,

we will focus on Serial Attached SCSI storage technology, specifically for Dell's PowerVault

MD1000 storage expansion enclosure and Dell's PERC 5/E RAID controller. Other storage

technologies such as SCSI or Fibre Channel, as well as topologies such as Network Attached

Storage (NAS) or Storage Area Network (SAN) are outside the scope of this document. All storage

applications will be treated independent of any specific host system or server.

Serial Attached SCSI (SAS)

The SCSI (Small Computing System Interface) protocol originated more than 20 years ago and is

used in the majority of server storage needs (e.g. storage that is internal to a server or physically

connected to a server in an external disk expansion enclosure). The market prevalence of SCSI

has created economies of scale making it one of the most affordable storage interconnect

technologies available today. Many businesses rely on SCSI physical disks to help deliver

extremely cost-effective and reliable storage. In fact, SCSI physical disks have advanced over the

years offering increased performance and more sophisticated features with each iteration.

However, given the inherent limitations of its parallel architecture, the current version of SCSI

physical disks, U320 or Ultra320, will be the last version of the traditional SCSI technology.

Serial Attached SCSI (SAS) is a major iteration of SCSI technology and introduces a host of

benefits when compared to older SCSI technology including,

Dramatic improvement in bandwidth performance

The first generation of SAS will support 3.0 Gbps (or 300 MB/sec) per "lane"

•

Ultra320 SCSI is the shared-bus architecture. SAS introduces a point to point topology

•

enabling systems with many physical disks to scale bandwidth far beyond the bandwidth

capacity of Ultra320 SCSI.

Figure 1: Parallel U320 SCSI bus versus point to point Serial Attached SCSI connection

SAS introduces the concept of port aggregation to storage interconnects. External storage

•

devices can connect via a x4 ("by four")wide-lane. Cabling aggregates four SAS lanes, each

operating at 3.0 Gbps, for a full external connection bandwidth of up to 12.0 Gbps on a single

connector.

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Up to320 MBps

Up to 3.0 Gbps per link

VER A00

5/06/2005