Netgear EDA 500 User Manual
Basic LUN Concepts
The volumes on your ReadyNAS can be divided into shares and logical unit numbers (LUNs), both of
which are logical entities on one or more disks. Shares and LUNs enable you to organize data in a volume
by type, group, user, department, and so on. A single volume can contain multiple shares and LUNs.
which are logical entities on one or more disks. Shares and LUNs enable you to organize data in a volume
by type, group, user, department, and so on. A single volume can contain multiple shares and LUNs.
LUNs are SAN (storage area network) data sets that allow data transfer and storage over iSCSI and Fibre
Channel devices. The ReadyNAS supports iSCSI devices only. Each ReadyNAS system supports up to
256 LUNs. The local admin page displays LUNs in the following way:
Channel devices. The ReadyNAS supports iSCSI devices only. Each ReadyNAS system supports up to
256 LUNs. The local admin page displays LUNs in the following way:
Figure 6. Thin LUN
Figure 7. Thick LUN
Each LUN is configured independently of other LUNs that reside on the same volume. You can configure
settings such as compression, protection, provisioning, LUN size, and access rights. You can also specify
whether and how often a snapshot is created. These settings are explained in the following sections.
settings such as compression, protection, provisioning, LUN size, and access rights. You can also specify
whether and how often a snapshot is created. These settings are explained in the following sections.
Thin and Thick Provisioning
You can specify the size of a LUN in two ways:
•
Thin. A thin LUN lets you overallocate its size. That is, you can assign a LUN size that is larger than
the size of the volume. Even though you specify the size of a thin LUN when you create it, storage
space is assigned on demand instead of up front. This method greatly improves the utilization rate of
the LUN because storage space is assigned only as data is written to the LUN. However, the size of
the LUN is reported as the total storage space that you specify when you create the LUN.
You can expand a volume as needed (if necessary, adding disks in the process) without expanding
the size of the LUN and therefore, without disconnecting users. Make sure that you watch the volume
capacity of the volume on which the overallocated LUN resides so you do not run out of storage space
unexpectedly.
the size of the volume. Even though you specify the size of a thin LUN when you create it, storage
space is assigned on demand instead of up front. This method greatly improves the utilization rate of
the LUN because storage space is assigned only as data is written to the LUN. However, the size of
the LUN is reported as the total storage space that you specify when you create the LUN.
You can expand a volume as needed (if necessary, adding disks in the process) without expanding
the size of the LUN and therefore, without disconnecting users. Make sure that you watch the volume
capacity of the volume on which the overallocated LUN resides so you do not run out of storage space
unexpectedly.
NETGEAR recommends that you do not use an overallocated LUN for storage of
critical data. Instead, use a thick LUN.
critical data. Instead, use a thick LUN.
Note:
•
Thick. All storage space that you specify when you create a thick LUN is allocated up front and the
storage space is reserved on the volume. Snapshots, other LUNs, and shared folders on the volume
cannot consume storage space that is reserved. The size of the LUN is reported as the total storage
storage space is reserved on the volume. Snapshots, other LUNs, and shared folders on the volume
cannot consume storage space that is reserved. The size of the LUN is reported as the total storage
LUNs
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ReadyNAS OS 6.2