Dell PowerVault MD1120 - Manual (Page 6)

A REFERENCE GUIDE FOR OPTIMIZING DELL™ POWERVAULT™ MD1XXX FAMILY SAS SOLUTION VER A02
PAGE 6 6/16/2008
• 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.
Figure 2: Bandwidth improvement with SAS port aggregation
Improved capacity scalability
• SAS allows for port expansion, enabling the ability to “daisy-chain” storage enclosures for
dramatic improvements in capacity scalability. With Ultra320 SCSI, systems were limited to a
maximum of 16 devices on a single SCSI channel. This typically translated to maximum of 14
physical disks connected to a single SCSI channel on a RAID controller. With SAS expansion,
a single SAS port can be expanded out to multiple SAS devices (similar to how Ethernet hubs
can expand a single Ethernet connection into multiple devices).
Other important changes to keep in mind about SAS:
• SAS continues to use the SCSI command sets for driver & software compatibility.
• SAS is not backwards compatible with Parallel SCSI.
One parallel SCSI cable
Up to 320MB/s
(equal to 2.56Gb/s)
One x4 SAS cable
12 Gb/s performance