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Network-attached storage is essentially an optimized or specialized file system running on an appliance or an appliance integrated with storage. Most midrange and enterprise-class NAS systems provide snapshot capabilities, including those with proprietary operating systems and the wide variety of NAS systems that are based on Microsoft Windows Storage Server.
There's a lot to like about NAS-based snapshotting, including a common standard for all of the physical and virtual servers, desktops and laptops that connect to the NAS device. It's also very easy to implement, operate and manage. NAS-based snapshot technology tends to be integrated with Windows Volume Shadow Copy Services (VSS), as well as with backup servers and their agents. Some NAS vendors have their own agents for non-Windows structured data applications. Other NAS snapshot offerings include data deduplication (EMC Corp., FalconStor Software Inc. and NetApp), and some even offer thin snapshot provisioning that minimizes the amount of storage reserved for snapshots.
But there's a price to pay for the convenience and added features: fairly hefty software licensing and maintenance charges that are often system or capacity based. NAS systems tend to proliferate in most companies and, as they do, the number of touchpoints required for snapshots will also increase, making operations and management more complex.
Storage array-based snapshots
The advantages of using snapshotting that comes with the storage array operating system are similar to those of NAS-based snapshots. They provide a common standard and touchpoint for all of the physical and virtual servers, desktops and laptops connected to the array, and are easy to implement, operate and manage. And, like NAS, many storage arrays integrate their snapshot technology with Windows VSS, as well as with backup servers and their agents. Some vendors even provide their own agents for non-Windows structured data applications.
The drawbacks include hefty license and maintenance fees, lack of integration with non-Windows-based structured data applications and increasing complexity as the number of storage systems increases.
Snapshots with storage virtualization appliances
Storage virtualization appliances are primarily SAN based with the exception of F5 Network Inc.'s Acopia ARX, which is file (NFS) based. Other examples of virtualization appliances (or storage systems that incorporate virtualization) include Cloverleaf Communication Inc.'s Intelligent Storage Networking System (iSN), DataCore Software Corp.'s SANsymphony and SANmelody, EMC's Celerra Gateway blades, FalconStor's IPStor, Hewlett-Packard's XP series, Hitachi Data Systems' Universal Storage Platform V/VM, IBM's SAN Volume Controller, LSI Corp.'s StoreAge Storage Virtualization Manager (SVM) and NetApp's V-Series storage controllers.
Storage virtualization approaches to snapshots have the same advantages as storage array- and NAS-based snapshots, but offer others as well. They provide a common standard and point of management for multiple storage systems from a single or several vendors, aggregating them into fewer or just one image. This greatly simplifies snapshot management, operations and training.
The negatives related to storage virtualization-based snapshots are a bit different. These devices will add some transaction latency, even those that have split-path architectures, which ultimately affects app response time. It also complicates troubleshooting and has the potential to exacerbate multivendor finger-pointing. And while the additional hardware or software comes with a price, it may be offset by lower software license or maintenance fees for the virtualized storage.
This was first published in October 2009