Understanding LUNs on vFilers

What LUNs are

LUNs are portions of filer storage that, when exported, look and act to the importing host like local disks. (They are sometimes referred to as "virtual disks.") Data on a LUN can be managed at the block level (for example, by a database manager) as well as at the file level. A LUN is the basic unit of storage in a Storage Area Network (SAN).

What is supported on vFilers

Data ONTAP allows you to create and manage a separate set of iSCSI LUNs and initiator groups (igroups) on each vFiler. For detailed information about iSCSI LUNs, see the Block Access Management Guide for iSCSI.

What is not supported on vFilers

FCP LUNs are supported only on the hosting filer, not on vFilers. For detailed information about FCP LUNs, see the Block Access Management Guide for iSCSI. This means

You can create FCP igroups only on the hosting filer.
FCP-connected hosts can access only those LUNs that are owned by the hosting filer.
The fcp command does not recognize vFilers.
You can create only iSCSI igroups on vFilers; you cannot create FCP igroups on vFilers.

iSCSI LUNs and igroups on vFilers

From the point of view of a host importing LUNs, a vFiler looks and acts just like a filer; administrators of those hosts normally do not even need to be aware that the LUN resides on a storage unit owned by a vFiler. But you, as the vFiler or hosting filer administrator, need to be alert to some special considerations.

Be aware of the following points when you manage LUNs on a filer on which a MultiStore license is enabled:

You must create and manage LUNs from the vFiler that owns the storage unit that contains the LUNs.
For instructions for switching the console to the context of a vFiler, see Executing commands and setting options for vFilers.
A vFiler is aware only of those LUNs in the storage units it owns. When executed on a vFiler, the lun show command displays only that vFiler's LUNs.
Ownership of LUNs changes with the ownership of the storage unit that contains the LUNS.
LUNs must be unmapped before the storage unit containing them can be moved. This means you must unmap all affected LUNs before doing any of the following:
- Assigning storage that contains LUNs to a vFiler when you create the vFiler or later
- Destroying a vFiler that owns storage that contains LUNs
- Moving storage that contains LUNs from one vFiler to another, or between a vFiler and the hosting filer
If you try to move a storage unit without unmapping the LUNs it contains, the operation fails. See the appropriate block access management guide for instructions for unmapping LUNs.

Note
You do not need to unmap LUNs when you migrate a vFiler or replace it for disaster-recovery purposes. For more information, see Chapter 6, Disaster Recovery and Data Migration.
igroups are owned by the vFiler on which they are created.
As with LUNs, a vFiler is aware only of those igroups that it owns. When executed on a vFiler, the igroup show command displays only that vFiler's igroups.
LUNs must be mapped to igroups owned by the vFiler that owns the LUNs.
Each vFiler has its own name space for LUNs and igroups.
- igroups on different vFilers can have the same initiator.
- LUNs on different vFilers can have the same LUN ID.
When you migrate a vFiler or replicate it for disaster-recovery purposes, LUNs owned by the vFiler are also migrated or replicated, along with their maps, igroups, and iSCSI configuration (the node names and the state of the iSCSI service). iSCSI authentication is not migrated or replicated.
For more information, see Chapter 6, Disaster Recovery and Data Migration.

The iSCSI service on vFilers

In general, the iSCSI service operates on individual vFilers, treating them as though each were a physical filer. But for the iSCSI software adapter itself (iswt), and the commands that manage and report on it and the underlying network interface cards (NICs), operate on the hosting filer. This is because an iSCSI adapter on a filer has only one identity (there are no vFiler-specific adapter names) and so there is only one set of iSCSI sessions and statistics.

This section lists what is filer-based and what is vFiler-based. For more information on the iSCSI service, see the Block Access Management Guide for iSCSI.

The following items are based on the hosting filer:

The iswt command, which you use to manage the iSCSI service on the filer's NICs, operates on the hosting filer, not on individual vFilers. The iswt driver allows the filer to be accessed as an iSCSI target device over the filer's standard network interfaces.
If iSCSI is licensed on the hosting filer, the iSCSI service is started by default during vFiler setup.
Although most iSCSI subcommands operate specifically on each vFiler on which they are executed, the iscsi stats command displays statistics by hosting filer and iSCSI adapter.

The following group is based on the individual vFiler:

The iSCSI protocol can be allowed and disallowed, and the iSCSI service can be started and stopped, for each vFiler.
The adapter is online or offline for each vFiler, depending on whether the iSCSI service is running or stopped on that vFiler.
Each vFiler has its own iSCSI node name, which includes the vFiler's uuid.
Portal groups are defined for each vFiler.
iSCSI subcommands operate specifically on each vFiler on which they are executed, except for the iscsi stats command.
You configure iSCSI security separately for each vFiler.
This includes setting the default authentication mode: none, deny, or Challenge Handshake Authentication Protocol (CHAP). For more information abut CHAP, see the Block Access Management Guide for iSCSI.
- In the case of CHAP, there is a separate list of initiators and passwords for each vFiler.
You can configure iSNS (iSCSI's naming service) separately for each vFiler.
Specifically, you can use iscsi isns subcommands on each vFiler to
- Configure which iSNS server to use.
- Turn iSNS registration on or off.
On creation, a vFiler's iSNS configuration is in the UNCONFIGURED state, no matter what the state is on the hosting filer.

For more information, see the na_isci man page.