Logical units and target ports on Xiotech Emprise systems

On Xiotech Emprise systems, logical units (LUs) are enumerated devices that have the same characteristics as logical unit numbers (LUNs).

LUNs

An Xiotech Emprise logical unit is referred to as a volume.

A single Xiotech Emprise volume can potentially consume the entire capacity that is allocated for SAN Volume Controller managed disk groups, but it cannot exceed the SAN Volume Controller 2 TB LUN size limit. Any LUN that is 2 TB or larger is truncated to 2 TB, and a warning message is generated for each path to the LUN.

LUN IDs

LUNs that are exported by Xiotech Emprise systems are guaranteed to be unique. They are created with a combination of serial numbers and counters along with a standard IEEE registered extended format.

LUN creation and deletion

Xiotech Emprise LUNs are created and deleted by using either the Xiotech Emprise Storage Management GUI or CLI. LUNs are formatted to all zeros at creation.

When a new LUN is created, the Xiotech Emprise system begins a background zeroing process. If a read operation comes in to an area that has not been processed yet, the system returns zeros as a read response. This is the normal procedure. If a previous LUN with data was in that storage area, it is zeroed out. If a non-zeroed-out area gets read, the system returns zeros if it has not been written to yet.

LUN presentation on Xiotech Emprise systems

Xiotech Emprise LUNs are presented to the SAN Volume Controller interface using the following rules:

LUNs can be presented to one or more selected hosts.
Configuration is easier if you create one host name for the SAN Volume Controller.
No individual LUN volume on the Xiotech Emprise system can exceed 2 TB in size.
For the managed reliability features to be effective on the Xiotech Emprise system, use either RAID 1 or RAID 5 when you create volumes.
The write-back and write-through cache options are available depending on the performance requirements on each individual LUN. Generally, write-back caching provides the best performance.
Although either Linux® or Windows® can be used, Linux is recommended for volumes that are intended for use on the SAN Volume Controller.

To present Xiotech Emprise LUNs to the SAN Volume Controller, follow these steps:

On the Xiotech Emprise system, create a single host name for the SAN Volume Controller and assign all SAN Volume Controller host bus adapter (HBA) ports to that host name as shown in Table 1.

Table 1. Host information for Xiotech Emprise
Name	Operating system type	HBA ports	Mapping
SVC_Cluster	Linux	500507680130535F 5005076801305555 500507680140535F 5005076801405555	Volume01 (lun:1) Volume02 (lun:2)

When you create new volumes that are intended for use on the SAN Volume Controller, assign them to the host name that is used to represent the SAN Volume Controller.

Special LUNs

The Xiotech Emprise storage system does not use a special LUN. Storage can be presented by using any valid LUN, including 0.

Target ports on Xiotech Emprise systems

Each Xiotech Emprise system has two physical fibre-channel ports. They are, by default, intended to provide failover or multipath capability. The worldwide node name (WWNN) and worldwide port name (WWPN) are typically similar, such as in the following example:

WWNN	20:00:00:14:c3:67:3f:c4 
WWPN	20:00:00:14:c3:67:3f:c4 
WWPN	20:00:00:14:c3:67:3f:c5

LU access model

The Xiotech Emprise system has no specific ownership of any LUN by any module. Because data is striped over all disks in a DataPac, performance is generally unaffected by the choice of a target port.

LU grouping

The Xiotech Emprise system does not use LU grouping; all LUNs are independent entities.

LU preferred access port

There are no preferred access ports for the Xiotech Emprise system.

Detecting ownership

Ownership is not relevant to the Xiotech Emprise system.