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ISS Technology Update
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
HP StorageWorks Modular Smart
Arrays
HP ProLiant Smart Array RAID
controllers
URL
http://h18006.www1.hp.com/storage/disk_storage/msa_diskarrays/
index.html
http://h18004.www1.hp.com/products/servers/proliantstorage/array
controllers/index.html
Volume 8, Number 5
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