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Demartek Low Latency Evaluation of Fibre Channel, iSCSI and SAS Host Interfaces

14 October 2011

By , Demartek President

IT professionals see Solid State Disk (SSD) products as a means to obtain higher performance and better response times. Having higher IOPS and shorter latencies than HDD, SSDs are being deployed in external storage arrays in conjunction with, or replacing HDDs. While high IOPS is frequently the metric for assessing drive and array performance, in many cases latency is equally as important. For example, in an OLTP application, short response times are critical. A transaction may require many successive queries to a database, where each query depends on answers returned from the previous query. User response times are entirely dependent on how quickly storage can return answers to the queries.

While SSDs can enable short response times, the connection to the storage array may limit these responses. An increasing number of current generation storage systems are providing multiple types of host interfaces for the same storage system, giving customers a wide variety of choices for connectivity to these storage systems. Block host interfaces, including Fibre Channel, iSCSI and SAS are all becoming increasingly available for today’s storage systems.

LSI commissioned Demartek to compare four block interface and speed combinations on the same NetApp E2600 storage system for basic performance. These four host interfaces were:

At first glance, one might assume that the interfaces with the highest line rates would provide the best overall performance, but we found that this was not the case.

We found that the best overall performance for this storage system was with the 6Gb SAS host connection, followed very closely by the 8Gb Fibre Channel host connection. This is due to the low latency characteristics for 6Gb SAS connections, as measured from the application host server. Although 6Gb SAS has a lower line rate than 8Gb Fibre Channel or 10Gb iSCSI connections, its overall protocol overhead is lower than the other interfaces tested, and makes an excellent choice as a host interface for storage systems.


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Demartek Low Latency Evaluation