As NAS systems proliferate, the amount of wasted
SearchStorage.com has already covered the issues involved in purchasing a NAS product. Now here are the criteria for purchasing dedicated NAS appliances from vendors such as agami Systems, Dell Inc., EMC Corp., IBM, ONStor Inc. and Sun Microsystems Inc.
Purchase sufficient storage capacity. Consolidation places more storage demands on fewer storage platforms, so a NAS intended for consolidation should at least meet the total storage of the systems being replaced, while providing headroom to accommodate foreseeable growth. If you're consolidating three NAS boxes with a total capacity of 10 TB, it's easy to start with a single 10 TB to 12 TB NAS system. But if growth rates are projected at 25% annually, your NAS environment may balloon to 35 TB over five years. Be sure to select a NAS that is expandable to that projected capacity. Here's a case where capacity planning tools will be a huge help.
Reliability and availability features. With more storage on fewer systems, those fewer systems need to be available and reliable. When selecting NAS for consolidation, pay attention to the RAID levels for disk protection. RAID 5 is adequate for SAS disks, but you'll need RAID 6 (dual parity) for NAS systems running SATA disks. In addition, components, such as power supplies and controllers, must be redundant and multiple network ports should support failover. It's vital to eliminate single points of failure.
NAS connectivity and bandwidth. One disadvantage to consolidation is that more network traffic is concentrated into one place. This can hurt storage performance if either the network or the consolidated storage system cannot meet traffic demands. Up-front testing and evaluation can reveal potential connectivity problems. Most connectivity issues can be overcome by aggregating multiple Ethernet ports into a single channel, coupled with changes to the local network itself. NAS vendors can make connectivity and bandwidth recommendations.
Internal storage performance. Performance isn't just about getting data into or out of the NAS box, it's also a matter of getting data to or from the disks. Consolidation means more user storage requests at the same box, so measure the disk IOPS and data throughput compared to multiple separate boxes to ensure adequate disk performance under load. Pay attention to the behavior of mission-critical data types or storage service levels may be affected, which reduces the benefit of consolidation.
Evaluate the potential for clustering. Some high-performance NAS systems use clustering to improve capacity and connectivity. In effect, multiple NAS boxes are connected to the network and each other using a fast interface -- each box bears part of the traffic burden while sharing storage as if it were a single pool. When more storage or additional connectivity is needed, storage administrators buy another box and add it to the cluster. Note: Clustering is not synonymous with performance, and some high-performance NAS boxes do not require clustering. Clustering is a good tactic for organizations that do not want the initial capital expense of a large NAS and prefer to add capacity and connectivity as needed over time.
Power conservation. One aspect of green storage is consolidating storage systems to reduce overall power consumption in the data center. However, having fewer boxes often means having more redundant components and having to hold more disks. When considering NAS consolidation, study your options for power conservation. It may be possible to reduce power to idle disks (or spin them down entirely). Just remember that reducing disk power will also reduce disk performance, so balance the power/performance tradeoff.
Scope of management tools. Most NAS systems come bundled with a suite of management tools to handle tasks, such as backups, snapshots, replication and data migration. Test each tool for compatibility with other data center hardware. Also, examine your existing management tools for compatibility with the new NAS. Reducing the number of tools will ultimately simplify management.
Plan for hardware and software maintenance. The cost of NAS is more than just the initial purchase price. Both the hardware and the bundled software require periodic maintenance or upgrades, which increase total cost of ownership (TCO). When comparing costs, be sure to include these types of added expenses over the service life of the system.
Specifications are provided for the following NAS products:
This was first published in February 2008