HP StorageWorks 2/16V ISS Technology Update Volume 8, Number 5 - Page 7

ISS Technology Update Volume 8, Number 5 of the existing 3-Gb/s SAS interface. Therefore, for directly attached storage configurations, there is currently no performance benefit to using 6-Gb/s SAS drives attached to 6-Gb/s-capable disk controllers. Interoperability of 6 Gb/s drives with 3 Gb/s drives Six-Gb/s SAS drives are completely interoperable with 3-Gb/s drives. With the SAS interface standard, each drive is connected to the array controller using a separate point-to-point link, allowing the controller to communicate with each drive independently and at its own link speed. As a result, 6-Gb/s drives do not incur any performance penalty when mixed with 3-Gb/s drives on a 6-Gb/s capable array controller. Six-Gb/s drives can be attached to 3-Gb/s controllers, but they will operate using the 3-Gb/s SAS channel. 6 Gb/s SAS drives and Modular Storage Arrays Six-Gb/s SAS drives will provide definite performance benefits when used with next-generation HP Modular Storage Arrays (MSAs). MSAs provide external storage that is attached to the server's storage controller using a SAS wide port consisting of four SAS interface channels. MSAs then use SAS Expanders to support large numbers of drives across this connection. When the disk I/O for these drives is aggregated across the four SAS channels, the channel bandwidth becomes an important consideration. With 3-Gb/s drives and SAS channels, the four channel SAS port will typically become saturated when the MSA is configured with eight to twelve drives. The next generation of MSAs, using 6 Gb/s drives and SAS channels, will be able to support up to twice this number of drives before the SAS wide port bandwidth becomes saturated. 6 Gb/s HP Smart Array controllers Introducing HP Smart Array controllers with 6-Gb/s SAS channels in the HP ProLiant G6 servers prepares the way for the next several generations of SAS drives. Maximum disk I/O has been increasing 30 to 40% with each disk drive generation and will soon outstrip the capabilities of the 3-Gb/s SAS channel. Disk controllers capable of supporting 6-Gb/s operation will be better able to support the increased throughput of these drives when they are introduced. Additional resources For additional information on the topics discussed in this article, see these resources: Resource URL HP StorageWorks Modular Smart Arrays HP ProLiant Smart Array RAID controllers http://h18006.www1.hp.com/storage/disk_storage/msa_diskarrays/ index.html http://h18004.www1.hp.com/products/servers/proliantstorage/array controllers/index.html 7