Logical units and target ports on RamSan systems

Partitions on RamSan systems are exported as logical units (LUs) with a logical unit number (LUN) that is assigned to the partition.

LUNs on RamSan systems

RamSan systems are shipped with a particular capacity of user space, which depends on the model. A partition with this capacity is known as a logical unit.

RamSan systems can export up to 1024 LUNs to the Storwize V5000 through various exported FC ports. The maximum logical-unit size is the full, usable capacity of the RamSan system.

LUN IDs

RamSan systems identify exported LUs through identification descriptors 0, 1, and 2. The EUI-64 identifier for the LU is in the CCCCCCLLLLMMMMMM notation where CCCCCC is the Texas Memory Systems IEEE Company ID of 0020C2h, LLLL is the logical unit handle, and MMMMMM is the serial number of the chassis. The EUI-64 identifier is available on the detailed view of each logical unit in the GUI.

LUN creation and deletion

RamSan LUNs are created, modified, or deleted either by using a wizard tutorial in the GUI or by entering a CLI command. LUNs are not formatted to all zeros upon creation.

To create a logical unit, highlight Logical Units and select Create toolbar. To modify, resize, or delete an LU, select the appropriate toolbar button when the specific logical unit is highlighted in the navigation tree.

Note: Delete the MDisk on the Storwize V5000clustered system before you delete the LUN on the RamSan system.

LUN presentation

LUNs are exported through the available FC ports of RamSan systems by access policies. Access policies are associations of the logical unit, port, and host. A RamSan system requires that one of the three items is unique across all available access policies. LUNs that are to be presented to Storwize V5000 must be presented to all node ports in the system through at least two ports on the RamSan system. Present each LU to the Storwize V5000 on the same LUN through all target ports.

To apply access policies to a logical unit, highlight the specific logical unit in the GUI and click the Access toolbar button.

Special LUNs

The RamSan system has no special considerations for logical unit numbering. LUN 0 can be exported where necessary. In one RamSan model, a licensed Turbo feature is available to create a logical unit up to half the size of the cache to keep locked in the DRAM cache for the highest performance. No identification difference exists with a Turbo or locked LUN as opposed to any other LUN ID.

Target ports on RamSan systems

A RamSan system can house 4 dual-ported FC cards. Each worldwide port name (WWPN) is identified with the pattern 2P:0N:00:20:C2:MM:MM:MM where P is the port number on the controller and N is the address of the controller. The MMMMMM represents the chassis serial number.

The controller address is shown in the following code:

04:  FC-1
08:  FC-2
0C:  FC-3
10:  FC-4
14:  FC-5

Port 2B has a WWPN of 21:08:00:20:C2:07:83:32 for a system with serial number G-8332. The same system has a worldwide node name (WWNN) of 10:00:00:20:C2:07:83:32 for all ports.

LU access model

On a RamSan system, all controllers are Active/Active on a nonblocking crossbar. To avoid an outage from controller failure, configure multipathing across FC controller cards in all conditions. Because all RamSan systems are equal in priority, you gain no benefit by using an exclusive set for a specific LU.

LU grouping

The RamSan system does not use LU grouping.

LU preferred access port

RamSan systems have no preferred access ports because all ports are Active/Active across all controllers.

Detecting ownership

Ownership is not relevant to the RamSan system.