NAS system buying decisions


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Storage efficiency

Features and capabilities that allow you to store more data on physical disks should be a central piece of any storage array evaluation. The cost savings of having to buy less physical storage can be significant and can easily offset higher acquisition costs. In other words, a more expensive NAS may cost you less over its lifetime than a less-expensive one with inferior storage efficiency features, such as thin provisioning, efficient snapshots, thin clones, deduplication and compression. Implementation and efficacy of these features vary among NAS products. One area of differentiation is the granularity at which these features operate. In the majority of NAS systems, they’re applied to volumes, but in some they can be applied to directories or even files. “The EMC Isilon supports snapshots, replication and quotas at a file and directory level,” said Sam Grocott, vice president of marketing at EMC Isilon.

The following NAS storage efficiency features should be considered to minimize physical storage requirements.

Thin provisioning. The ability to allocate more storage than is physically available is pertinent to achieving high storage utilization. This is especially important in systems that support both file- and block-based protocols, where thin provisioning enables volumes and NAS pools to be sized independently of actual physical storage, and where physical storage is assigned from a common storage pool on an as-needed basis. Without thin provisioning, sufficient physical storage has to be allocated to each volume and storage pool ahead of time. In systems that support thin provisioning, physical storage is allocated dynamically when needed.

Efficient snapshots. Snapshots in NAS systems are invaluable for data protection. They’re scheduled to be taken periodically and can optionally be replicated to other NAS systems for disaster recovery (DR) or other data protection purposes. Supported by most contemporary NAS systems, efficient snapshots copy data changes and use a system of pointers to reference the initial full snapshot. Efficient snapshots not only save valuable disk space, but also reduce the time it takes to complete them, minimizing the performance impact while snapshots are taken.

Thin clones. Relevant in NAS systems that support block-based protocols, thin clones require little to no storage on creation. Similar to efficient snapshots, thinly cloned volumes refer to the original volume via pointers. Only data on the cloned volume that changes needs to be stored. Pioneered by NetApp with FlexClone, thin clones are now supported by a growing list of NAS vendors.

Deduplication and compression. Standard in backup and archival products, data deduplication and compression are becoming more prevalent on primary storage systems. While support for deduplication in NAS storage is still sparse, it can be implemented as a post-process scheduled task or in real-time. For instance, deduplication in NetApp filers can be enabled on a per-volume basis and is performed by a scheduled process that deduplicates 4 KB blocks of data, usually during off hours. On the contrary, the Oracle Sun ZFS Storage 7000 series performs deduplication in real-time while data is written to disk.

Automated storage tiering. The ability to keep active data on fast, expensive storage and move inactive data to less-expensive slower tiers helps to limit the amount of expensive tier-1 storage needed without significantly impacting performance. For any NAS system you consider, data movement between the different tiers (solid-state storage, fast SAS tiers and slower, high-capacity SATA tiers) should be automatic with block- or byte-level granularity rather than the volume-level granularity at which data is moved. The more granular, the better. Some systems, like EMC’s Fully Automated Storage Tiering (FAST), depend on policies that define when data should be moved; others, like NetApp and Oracle (in the Sun ZFS Storage 7000 series), advocate that the storage system should be smart enough to automatically keep data on the appropriate tier without requiring user-defined policies.

This was first published in November 2011

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