ICT SSDs
These latency classes are inherent in classic NAS architecture and understanding the issue and how flash can address them is vital for both a successful upgrade and delivering a successful longer-term storage strategy.
As an organisation’s data grows and the capacities of disk drives become bigger and bigger, the amount of time it takes to access a given file increases. Existing solutions to this problem have been less than ideal — NAS systems have moved to higher-speed (10K and 15K RPM) disk drives and sometimes, for an extra increment of speed, they short stroke them (that is, use only a fraction of their capacity) in order to read and write data off them faster. This type of disk overprovisioning takes up a lot of physical space in the datacentre, plus all that rotating mass generates heat and consumes a lot of electricity. Even the newest drives are relatively slow when compared with memory like NVRAM and DRAM, but replacing all the hard disk storage in a NAS system with semiconductor memory would be prohibitively expensive.
Another common issue faced by classic NAS systems is storage filer CPU latency. As all file-access requests pass through the storage filer, the embedded CPUs within the filers can cause another form of latency. If more I/O requests hit the filer than its CPU(s) can handle, queuing occurs and application performance slows to a crawl. The only reliable way to ensure that you get good performance with the classic NAS architecture is to use storage controllers with high- performance CPUs within these systems. Packing a storage controller full of high-end CPUs gives you a performance boost today, but it doesn’t scale unless you swap out filers, which is an expensive option.
The last performance issue is induced by the network. In a modern business environment, remote offices that may be hundreds or even thousands of miles away from the organisation’s datacentres require data to be sent over the network, which is subject to propagation delay that degrades the user experience. The physical bandwidth between the sites may also be limited and could also cause network throughput bottleneck issues. Encryption can further slow down transfer rates due to the processing overhead to scramble the protocols and payloads. For some organisations, data needs to reside within a central physical location for security, compliance or convenience, and the network latency issue becomes significant, but not insurmountable with a bit of re-architecting of how data is distributed and where data resides. So the combination of hard disk latency, storage CPU issues and the wide-area-networks (WAN) together can cause a major barrier to improving storage, but the clever use of flash filers can solve many of these issues in an elegant fashion.
Introducing edge filers Even though SSD prices have dropped significantly, compared to spinning media, chip-based memory in all its forms is still up to 30 times more expensive than legacy disk drives. Simple replacement of all spinning disks for chip-based equivalents is not financially viable. Instead, in Avere’s approach to NAS optimisation, a flash-based “edge” filer can shoulder the bulk of the processing load at high speed, while the high-capacity rotating storage back at the Core filer holds the bulk of the data that isn’t currently being accessed.
An Edge filer requires updating the traditional data management model to take advantage of the performance advantages of flash. The technology overcomes the traditional and costly approach of adding larger and more expensive controllers and over provisioning CPU and all types of high-speed storage media to boost performance. Instead, an Edge filer sits in the communication path between the user and the NAS Core filer at a location that is nearest to the user. If the user is located at a remote site and therefore at a distance from the datacentre where the NAS Core filer resides, you can largely eliminate WAN latency by placing the Edge filer physically close to the user at the remote site.
Since the Edge filer contains the hottest data, which is being accessed most frequently, the round trip transit time from the user to the data is minimised. The long trip back to the NAS for the cold data needs to be taken only a small fraction of the time, and overall performance is almost as good as it would be if the datacentre were right next door to the remote facility. Edge filers can include a mix of SSD and Flash memory as well as SAS drives to form a high performance Edge filesystem cache that sits in front and
S12
www.snseurope.info I Winter 2013
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