If you've ever had a SAN, you know provisioning storage is a complex, error-prone process and things don't always...
go exactly as planned. The result is often "stranded" storage--capacity that for one reason or another isn't accessible to an array.
There are three basic types of stranded storage, says Paula Dallabetta, marketing director at CreekPath Systems, a storage management software vendor:
- Raw storage that's never been configured.
- Configured storage that points to nothing.
- "Orphaned" storage-- storage that was presented to a server, but was never tied to a file system or volume manager.
There are many reasons storage gets stranded, says Ed Palmer, senior director, product management at storage resource management (SRM) vendor Storability Software. Examples include improperly zoned fabrics and misconfigured LUN security software. Improperly updated host configuration files are also a culprit.
At the heart of the matter is poor administrative processes and follow-through. For example, if a server is decommissioned or migrated, admins will sometimes forget to reallocate its associated storage resources. Storage provisioned to an array that never gets assigned to a server is another common administrative lapse. In the same vein, when new switches are added to an environment, the switch zones may not be properly updated.
A big selling point of many SRM packages is that they'll help you ferret out stranded storage. According to Dallabetta, some CreekPath customers have recovered terabytes of stranded storage by running the firm's CreekPath Suite.
But can you forego an SRM package and find stranded storage on your own? Not surprisingly, SRM vendors don't recommend it. "Without that end-to-end view between the file system and the array, it's a very painful process," says Dallabetta. Furthermore, it may be hard to prove beyond a shadow of a doubt that the storage you do find is actually stranded. "If you're not sure, you don't want to risk taking out some critical app," she adds.
If it's any consolation, stranded storage may prove to be less of a problem in IP SAN environments, says David Dale, industry evangelist at Network Appliance, because "a lot of the issues that lead to stranded storage in a Fibre Channel environment don't exist in an IP network." For one thing, most IP SAN environments don't use host bus adapters, eliminating one step in the provisioning process. Furthermore, native IP security features such as challenge handshake authentication protocol (CHAP) remove the need to do port zoning on the switch, eliminating another potential point of failure.