Choosing Das Or San Attach; Dealing With Controller Failovers - HP P2000 G3 MSA Technical White Paper

Technical white paper | HP P2000 G3 MSA
Another suitable example of a high-availability storage system using a single controller configuration is where a host uses a
volume manager to mirror the data on two independent single-controller P2000 G3 storage systems. If one P2000 G3
storage system fails, the other P2000 G3 storage system can continue to serve the I/O operations. Once the failed controller
is replaced, the data from the survivor can be used to rebuild the failed system.
Note
When using a single-controller system, the controller must be installed in the slot A of the array.

Choosing DAS or SAN attach

There are two basic methods for connecting storage to data hosts: Direct Attached Storage (DAS) and Storage Area Network
(SAN). The option you select depends on the number of hosts you plan to connect and how rapidly you need your storage
solution to expand.
Direct attach
DAS uses a direct connection between a data host and its storage system. The DAS solution of connecting each data host to
a dedicated storage system is straightforward and the absence of storage switches can reduce cost. Like a SAN, a DAS
solution can also share a storage system, but it is limited by the number of ports on the storage system.
A powerful feature of the storage system is its ability to support four direct attach single-port data hosts, or two direct
attach dual-port data hosts without requiring storage switches. The P2000 G3 FC can also support two single-connected
hosts and one dual connected host for a total of three hosts.
If the number of connected hosts is not going to change or increase beyond four then the DAS solution is appropriate.
However, if the number of connected hosts is going to expand beyond the limit imposed by the use of DAS, it is best to
implement a SAN.
Tip
It is a best practice to use a dual-port connection to data hosts when implementing a DAS solution. This includes using dual-
ported hard drives for redundancy.
Switch attach
A switch attach solution, or SAN, places a switch between the servers and storage systems. This strategy tends to use
storage resources more effectively and is commonly referred to as storage consolidation. A SAN solution shares a storage
system among multiple servers using switches and reduces the total number of storage systems required for a particular
environment, at the cost of additional element management (switches), and path complexity.
Using switches increases the number of servers that can be connected. Essentially, the maximum number of data hosts that
can be connected to the SAN becomes equal to the number of available switch ports.
Note
The HP P2000 G3 FC supports 64 hosts.
Tip
It is a best practice to use a switched SAN environment anytime more than four hosts or when growth in required or storage
or number of hosts is expected.

Dealing with controller failovers

Since the P2000 G3 uses Unified LUN Presentation, all host ports see all LUNs; thus failovers are dealt with differently than
with the MSA2000 G1 (excluding the MSA2000sa G1).
FC direct-attach configurations
In a dual-controller system, both controllers share a unique node WWN so they appear as a single device to hosts. The
controllers also share one set of LUNs to use for mapping volumes to hosts.
A host can use any available data path to access a volume owned by either controller. The preferred path, which offers
slightly better performance, is through target ports on a volume's owning controller.
8