The key objective for organizations investing in flash is to make sure that they are getting the maximum performance out of their premium investment. This means making sure that the application and storage infrastructures are optimized for the near zero latent performance of this storage. Other than general purpose SAN buffer credits, there has been limited capabilities to optimize specifically for flash based LUNs (Logical Unit Numbers). With their recent announcement, Emulex is set to provide flash specific services designed to deliver maximum flash performance.
A side effect of flash based storage is that it is so fast that it exposes weakness and latency in the rest of the architecture. In mixed flash and hard disk drive (HDD) storage area networks (SANs) for example, I/O requests directed at the HDD storage can actually block an I/O request directed at the flash tier. This adds latency to the response time for the application requesting data from the flash based tier because it has to essentially wait for the HDD I/O to complete.
In a hybrid environment, a data center with a mixture of all-flash arrays and HDD arrays or an environment with a single system mixed internally with flash and HDD, there has been limited capability to provide priority to the workloads counting on flash performance. In these environments, a server either running a hypervisor or dedicated to an application, will typically connect to both a HDD based LUN and a flash based LUN. As mentioned above, there has been limited ability to prioritize access to the flash based LUN; meaning that the flash I/O can be delayed by HDD I/O.
Emulex’s ExpressLane Feature is designed to allow their Gen 5 FC Host Bus Adapters (HBAs) to provide higher priority to specific LUNs that the host is connected to. This is an important capability that should allow a significant improvement in performance in hybrid environments, which is the case in the overwhelming number of data centers.
In addition, Emulex’s Flash Services announcement also includes a capability called CrossLink. CrossLink is ideal for what is commonly called east-west traffic, or server to server communication.
An excellent example of this communication is virtual machine migration, especially when service side caching is being used. In these situations, it is ideal for the VMs cached data, or at least the metadata associated with the cache, to move with the VM as it is being migrated. The problem is this requires a consistent, low latency point to point communication that IP does not provide. CrossLink allows this point to point communication to happen over fibre which provides lossless high performance.
Storage Swiss Take
Flash allows data centers to create denser virtual environments (servers and desktops) and it allows for more scalable databases. Density enabled by flash storage enables cost reduction elsewhere in the data center that can more than cover the flash investment. Without the ability to run flash at its full potential, however, these returns may never be achieved. Flash aware fibre channel services should allow IT planners to fully exploit this potential and realize maximum ROI.