Are You Ready For High Speed Storage Interfaces?

A new wave of high speed storage interfaces is on the way offering improved storage I/O performance To see the expected performance improvement you have to do more than simply add drives with the new interface and install a host bus adapter in the server, you have to make sure every link in the I//O chain is ready.The high speed interfaces include 6 Gb/s SATA, SAS as well as 8Gb/s and 16Gb/s fibre. All of these are significant step levels up in storage I/O capabilities of the connection to your storage. The storage devices are ready for it thanks to technologies like wide striping and solid state disk. Fibre on the drive may be waining and 6Gb/s SAS/SATA seem like they will be the primary drive interface for the future. There may be a few demands for fibre in legacy enterprise storage systems until they can move over to SAS.

The dual ports, greater queue depth and lower latency of 6Gb/s SAS as well as its very interesting light networking capabilities can make it the ideal interface for larger enterprise storage and shared storage systems. As we discuss in our article "Solid-State Drive Connectivity Options" 6Gb/s SATA, while not dual ported and more latent, is less expensive and is also compatible with all the 3GB/s SATA ports that are readily available on existing servers although running at the slower speed, making the move to an SSD drive potentially easier if it has a SATA interface instead of a SAS interface

To get full benefit from 6GB/s or greater speeds you have to make sure other links in the performance chain are able to support the faster speeds. The first place to start is the server. Upgrading it involves more than just inserting a 6Gb/s controller card into a PCIe slot and connecting it to a 6GB/s drive. Many users do this and are disappointed to find no performance increase. A common culprit is the backplane of the server; it has to be able to support the faster transfer rate and many of them can't. If your server does not have the backplane to support this level a performance, it doesn't mean that you can't benefit from the faster drive technologies, just know that you are not going to reach rated speeds.

If you know the backplane is able to support 6GB/s or you are OK living with less than maximum performance, the next area to look is the application on the server. In fact before adding any hardware to the environment, you always want to check CPU utilization. If CPU utilization is relatively high, say more than 60%, then you more than likely don't have a storage performance problem, you have a processing problem. If the CPU utilization is relatively low but performance of an application is not what it needs to be then there is a good chance you have a storage performance problem.

We document how to diagnose exactly what the performance problem is in our Visual SSD Readiness Guide but the CPU is a good early indicator. 6GB/s storage devices will improve response time and in most cases decrease latency, both of which should help accelerate an application. From there you want to look at either increasing the number of disk drives in the RAID group or moving to solid state disk.

Performance troubleshooting is a circular chain, once you speed up one link you expose other links' weaknesses. You have to keep fixing each link until you get to the point where your performance problem is resolved.

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George Crump is lead analyst of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. Find Storage Switzerland's disclosure statement here.