S A S
E N D - U S E R G U I D E
6
Putting Serial Attached SCSI to Work for You
SAS Components and Systems
Host Bus Adapters:
SAS host bus adapters (HBAs) feature 300MB/s connections. Multiple ports increase the
total available bandwidth; as an example, an eight-port HBA would provide a total
bandwidth of 4800MB/s.
Another new feature to look for when choosing an HBA is the newest RAID level —
RAID 6. RAID 6 data protection offers twice the fault tolerance of RAID 5. A machine
protected by RAID 5 can only sustain the failure of one hard drive and is vulnerable to
data loss if another drive fails while the array is rebuilding and in the degraded mode.
A machine protected by RAID 6 can sustain two drive failures, and therefore is far more
available than other RAID levels. This is ideal for SATA environments which can be
susceptible to drive failure. The cost of RAID 6 is only one additional disk drive, a small
price to pay for this significantly improved protection.
Disk Drives:
One of the benefits of the SAS interconnect technology is its ability to support both SAS
and SATA drive types. This offers the flexibility to hit a price point with low-cost lower-
performance SATA drives, and also provide maximum performance and reliability using
SAS drives; achieving the right balance between cost, performance, and reliability.
SAS disk drives are dual-ported, like Fibre Channel drives. SAS drives are also rated at the
same reliability level as SCSI and FC hard drives, meeting your most demanding
reliability and availability needs.
SAS provides a high-speed, high-density alternative to SCSI. As such, the first places it is
being deployed will be in point-to-point solutions, such as DAS and clustered storage
scenarios. These first SAS topologies will deploy SAS internally while still relying on Fiber
Channel or iSCSI for interconnecting external storage enclosures.
Internal Enclosures:
SAS enclosures can accommodate SAS or SATA disk drives. Using SAS drives in an
enclosure provides highly reliable and highly available storage, suitable for primary
storage solutions. Initial capacity provided by a SAS enclosure can be easily increased
with SAS expansion arrays.
Using RAID 6 in conjunction with an enclosure provides higher availability levels than
RAID 5, making it suitable for primary storage even if lower-cost SATA disks are used
instead of SAS disks.
Expanders:
SAS expanders will be introduced and will enable external SAS storage enclosures to span
multiple host initiators and external enclosures. This will allow the creation of large scale
SAS-based solutions; expanding far beyond the number of drives and unit numbers SCSI
can support today. When coupled with RAID 6, these configurations can create high-
performance, highly scalable, and highly available solution sets.
External Storage Arrays with Internal SAS/SATA Disk Drives:
External storage arrays are currently available with SCSI, SATA, and FC disk drives.
Adding the capability of SAS drives provides additional flexibility to configure high-
performance, high-reliability solutions and/or low cost, high-density solutions,
depending on the intended application and reliability needs.
