Specifications

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Summary of Best Practices for Storage Area Networks

4.3 XIV

The main goal for the host connectivity is to create a balance of the resources in the

XIV Storage System. Balance is achieved by distributing the physical connections

across the Interface Modules. A host usually manages multiple physical

connections to the storage device for redundancy purposes by a SAN connected

switch. It is ideal to distribute these connections across each of the Interface

Modules. This way the host utilizes the full resources of each module that is

connected to and can obtain maximum performance. It is important to note that it is

not necessary for each host instance to connect to each Interface Module.

However, when the host has more than one connection to an XIV storage system, it

is beneficial to have the connections spread across multiple interface modules.

Although XIV storage systems supports up to twelve logical connections per host

server, the multipathing utility on the host server may not be able to fully utilize this

number of connections. Utilizing more than 12 Fibre Channel ports for host

connectivity will not necessarily provide more bandwidth. Best practice is to utilize

enough ports to support multipathing, without overburdening the host with too many

paths to manage. There are various key points when configuring the host for

optimal performance.

Because the XIV Storage System is distributing the data across all the disks an

additional layer of volume management at the host, such as Logical Volume

Manager (LVM), might hinder performance for workloads. Multiple levels of striping

can create an imbalance across a specific resource. Therefore, it is best to disable

host striping of data for XIV Storage System volumes and allow the XIV Storage

System to manage the data.

Based on the host workload, the maximum transfer size that the host generates to

the disk to obtain the peak performance may need to be adjusted. For applications

with large transfer sizes, if a smaller maximum host transfer size is selected, the

transfers are broken up, causing multiple round-trips between the host and the XIV

Storage System. By making the host transfer size as large as or larger than the

application transfer size, fewer round-trips occur, and the system experiences

improved performance. If the transfer is smaller than the maximum host transfer

size, the host only transfers the amount of data that it has to send.

Due to the distributed data features of the XIV Storage System, high performance is

achieved by parallelism. Specifically, the system maintains a high level of

performance as the number of parallel transactions occurs to the volumes. Ideally,