White Papers

5 Dell Storage PS Series Arrays: Scalability and Growth in Virtual Environments | TR1072
1 Introduction
The PS Series SAN architecture allows for mobility of storage volumes across the peer storage arrays. This
architecture also includes a Network Load Balancer (NLB) to redirect iSCSI login sessions to provide better
efficiency and bandwidth management to the SAN. As new array members are added to a storage pool, new
and existing volumes will load balance across the new members and the NLB will take advantage of newly
introduced controller network ports to load balance connections into the SAN. This flexibility gives the PS
Series SAN the ability to move data volumes seamlessly to any member or members in the group and
maintain iSCSI sessions to the members that share the volumes. When not managed properly, this flexibility
can also introduce growth and scaling issues that may not be of concern when initially deploying a PS Series
SAN.
In firmware 9.0.x, the connection count limitation that has been tested and validated is 1,024 per pool with
4,096 per group (with 4 pools). For a list of supported connections per firmware version, see Table 1. This
limitation is regardless of the actual number of members in the pool. Each member has to share all of the
page table information as well as connection information, so this number does not scale by adding or
subtracting members. This number is not a hard limit but a soft limit that was tested and validated. Exceeding
1,000 connections will generate errors in the logs and potentially dropped connections to volumes. Due to
scale and sizing, keeping these connection counts lower will generally result in easier growth of the SAN.
This document is designed to assist in planning and deploying hypervisor environments. This document also
addresses steps toward re-architecting an environment to help lower the overall number of connections to a
PS Series Group, and provides suggested improvements to current environments.
Supported PS Series Group connection counts by firmware version
PS Series firmware
PS6xxx storage
pool connection
limit
PS6xxx Group
connection limit
PS4xxx storage
pool connection
limit
PS4xxx Group
connection limit
Prior to v5.x.x
512
2,048
256
512
v5.x.x and newer
1,024
4,096
512
1,024
Note: Refer to http://www.eqlsupport.dell.com for more information on the technical specification of each
array family and the supported connection limits they offer.