Requirement for enabling gFilers to read from and write to LUNs

Storage subsystems must make LUNs available on ports

Before a gFiler can see LUNs on a storage subsubsystem, one or more LUNs must be created on the storage subsystem and then configured to be available (visible) to the gFiler on the ports to which the gFiler is connected. The process varies among vendors for how LUNs are created and made available to gFilers. The process also varies as to how access controls on LUNs are imposed. See the Gateway Series Getting Started Guide for your storage subsystem for details.

Logical relationship between gFilers and LUNs

gFilers use a software-based scheme to control access of gFilers to LUNs that a storage subsystem has made available. This scheme enables you to make changes at the software level that in typical systems can only be made in a fixed LUN-ownership scheme. The following illustration shows the relationship between the LUNs that are made available for gFilers on the storage subsystem and the gFiler configuration scheme.

With the gFiler software scheme, for a gFiler to read from or write to a LUN that the storage subsystem has made available, you must establish a logical relationship between the gFiler and the LUN through a gFiler command (disk assign). From the point of view of the Data ONTAP software, this logical relationship is referred to as disk ownership (because a gFiler considers a LUN to be a virtual disk). From the point of view of the storage subsystem, you can think about disk ownership as the gFiler owning the LUN. Only one gFiler can own a specific LUN; Data ONTAP writes data to the LUN to identify the gFiler that is the "owner."

Caution
The gFiler software-based scheme provides ownership control only for gFilers; it does not prevent a non-gFiler host from overwriting data in a LUN that a gFiler owns. Therefore, if a non-gFiler host is sharing an storage subsystem port with one or more gFilers, use LUN security on your storage subsystem to prevent gFilers and non-gFilers from overwriting LUNs.

Benefit of the disk ownership scheme

The primary benefits of the disk (LUN) ownership scheme are

You can leave LUNs unused until you need them. When you need them, you can use a command at the gFiler console to add them to the storage that the gFiler is using.
If you need to move data service from one gFiler to another because one gFiler is handling too much load, you can do so at the software level through a process that is transparent to users. You do not need to reconfigure hardware or the LUN access controls on the storage subsystem to change which gFiler is servicing data requests. Chapter 7, Managing Workload Distribution with SnapMover provides more information about the gFiler scheme of moving vFilers from one gFiler to another, which is based on the disk ownership scheme.