PS Series Architecture: MPIO with Devices That Have Unequal Link Speeds Dell Engineering June 2015 A Dell Technical White Paper
Revisions Date Description June 2015 Initial release THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND. Copyright © 2015 Dell Inc. All rights reserved. Dell and the Dell logo are trademarks of Dell Inc. in the United States and/or other jurisdictions. All other marks and names mentioned herein may be trademarks of their respective companies.
Table of contents Revisions ..................................................................................................................................................................................................2 Executive summary .............................................................................................................................................................................. 4 1 Best Practice for network interfaces in a PS Series SANs .................................
Executive summary A Best Practice when building a Dell™ PS Series SAN is to use equal network speed on all hardware attached to the SAN. This includes host ports, network switches and PS Series arrays. When this is not possible, the PS Series Multi-Path I/O (MPIO) software included with Windows®, VMware® and Linux® HIT kits attempts to optimize the resources present.
1 Best Practice for network interfaces in a PS Series SANs A Best Practice when deploying hosts and storage arrays on the same PS Series SAN is to utilize a common network speed throughout the environment. This includes host ports (NIC, offload cards or HBAs), network switching, and PS Series arrays. For example, to obtain the best results install 1GB components in a configuration using a 1Gb array (such as a PS6100) and 10Gb switches and host interfaces when using 10Gb capable arrays (such as the PS6210).
2 Multi-Path I/O MPIO uses redundant physical (or virtual) connections to deliver high availability to shared storage. Having multiple host connections, switches and SAN interfaces helps to eliminate single points of failure. Using MPIO, servers can send multiple I/O streams to SAN volumes concurrently.
The service periodically retrieves the current volume layout from the PS Series Group. It also monitors the iSCSI sessions and SAN topology and reconfigure the iSCSI session mesh when necessary (see Figure 1). Together, these components allow administrators to easily install and configure MPIO for iSCSI networks. The MPIO extensions, along with a redundant iSCSI hardware configuration, create the infrastructure needed for a completely fault tolerant and efficient MPIO solution.
3 Handling unequal network speeds The PS Series MPIO extensions attempt to optimize uneven resources when the Ethernet ports on the host and the Ethernet ports on a PS Series array group do not have identical network speeds. In other words, 10Gbps host ports paired with 1Gbps array ports, or 1Gbps host ports paired with 10Gbps array ports.
to 4Gbps (< 10Gbps) bandwidth. Again, all connections are further subjected to the Max Connections per Member and Max Connections per Volume limits and other limiting factors previously mentioned. 3.3 When host ports are slower than PS Series group ports When the host ports are slower than the PS Series group ports, the number of slower host ports limits the number of iSCSI connections. This applies with 1Gbps hosts and 10Gbps PS Series group ports.
3.4 Connection Examples Several examples of the number of connections created by the PS Series MPIO software are provided in Table 1. Each example depicts a different size PS Series group size. Pool limits or large configuration limits were not applied in these examples, nor do they depict mixed host interface configurations involving the use of 10Gbps and 1Gbps interfaces on a single host.
3.5 A complex example using variable speed host interfaces and limiting total connections per volume Variable speed host interfaces are interfaces where the bandwidth used can be set to less than the actual link speed of the device. In this case, the lower bandwidth set on the interface determines the number of connections rather than the maximum speed that the interface is capable of supporting. The MPIO software attempts to maximize the bandwidth available.
A MPIO extension controls per platform The PS Series MPIO extensions default values can be adjusted to provide control over the maximum number of total iSCSI connections per volume and the maximum number of iSCSI connections to each member from a host for a single volume. Refer to the Host Tools documentation for each platform for details on how to set these parameters.
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