What you will learn: Five items to consider before you select and implement a file virtualization appliance.
Operating in front of network file servers, file virtualization appliances create an abstraction layer between file servers and the clients that access them. The file virtualization layer catalogs files and file systems across multiple network file servers, and enables administrators to present a single, logical file
mount point for all network file servers that's accessible by all client servers. Once in place, network file servers continue to host file data and meta data while the file virtualization appliance provides advanced file management capabilities. File virtualization appliances provide the following major benefits: 1.) A global namespace that indexes files on network file servers. 2.) Excess storage capacity can be shared among network file servers. 3.) Data migrations that are transparent to end users and applications. 4.) Support for tiered storage infrastructures.
Consider the following five items when selecting a file virtualization appliance:
- In-band or out-of-band? In-band file virtualization appliances present a common, single interface for all network file servers. While they can simplify management and file migrations, in-band appliances can become a bottleneck if not sized appropriately. Administrators can usually deploy out-of-band file virtualization appliances with little or no initial disruption to their environment, but they may need to push out agents to servers or move in-band to perform file migrations.
- Global namespace. A global namespace is a central catalog of the files that reside on network file servers. Organizations that have NAS namespaces may need to switch from their current namespace to the one introduced by the file virtualization appliance.
- Appliance availability. If you plan to use a file virtualization appliance strictly to perform file migrations, availability isn't a concern because both in-band and out-of-band appliances permit failures without data loss. But if you're planning to permanently virtualize the environment and also take advantage of advanced functions like striping files across different file servers or aggregating network filer volumes, make sure the appliance's level of availability matches your company's service-level agreements.
- Filer volume sizes. File virtualization appliances are often used to consolidate file systems residing on multiple network file servers onto one file server during migrations. However, it's important to remember to keep file-system volumes at sizes that can be backed up within specified backup windows.
- Support for network filer APIs. File virtualization appliances don't diminish the value that NAS operating systems like EMC Corp.'s DART and Network Appliance Inc.'s Data Ontap deliver with such features as snapshots and file locking. When using these features, look for file virtualization appliances that integrate with these devices so policies may be set on the appliance to centrally manage these functions.
Check out the complete Storage magazine article, Rein in NAS with file virtualization.
Jerome M. Wendt is a storage analyst specializing in open-systems storage and SANs.