Release Notes

Deploying the MEM
7 Configuring and Installing the PS Series Multipathing Extension Module for VMware vSphere and PS Series | TR1074
The MEM achieves its performance gains by creating multiple iSCSI connections to each PS Series group
member that has a datastore volume. Assuming the MEM default settings are in use, and depending on the
configuration of the environment, there will be up to six iSCSI connections to a datastore volume. This is a
significant increase, when compared with the VMware Fixed path policy, which utilizes one iSCSI connection
per volume. This increase in connections must be planned at the time of deployment, and again as the
vSphere environment and its supporting PS Series storage environment scales.
To calculate the number of iSCSI connections that the MEM will consume in a particular environment, utilize
the following formula:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑆𝐶𝑆𝐼 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑖𝑜𝑛𝑠 = 𝐻 × 𝑉 × 𝑀 × 2
H = number of ESXi hosts
V = number of volumes
M = number of PS Series members in the pool (maximum value is 3)
2 = default number of iSCSI sessions per volume portion
For example, in a vSphere environment with eight ESXi hosts, and using a two-member PS Series pool for
hosting the ten volumes needed for virtual machines, the number of iSCSI connections would be:
8 x 10 x 2 x 2 = 320 iSCSI connections
While this is within the 1,024 iSCSI connection limit per pool of the firmware, it does not take into account
other iSCSI connections to the PS Series storage pool from other servers in the data center. Consider how
this virtual environment may grow in the future with respect to additional ESXi hosts, datastore volumes, and
additional PS Series members.
Using the SCSI commands, MEM and the array can communicate certain information. This enables the array
to notify the MEM of the number of total iSCSI connections to the pool from all sources. Should the number of
iSCSI connections to the pool begin to approach the limit, the MEM will reduce the number of iSCSI sessions
it is creating to the array, while still maintaining redundancy.
Depending on the overall environment and future requirements, changes may need to be made to one or
more of the following variables if there are concerns about the iSCSI connection count growing too large:
• The MEM parameters membersessions, volumessessions or totalsessions (see the
EqualLogic Multipathing Extension Module Installation and User Guide for details).
• Increasing the size of a given volume to allow more virtual machines to reside on it and reduce the
total number of volumes needed.
• Reconfigure larger clusters into multiple smaller clusters to reduce the number of hosts accessing
particular volumes and the number of iSCSI connections consumed.
• Reduce the number of PS Series members per pool and increase the number of pools to increase the
number of available iSCSI connections.
For more information on this topic, read the document, Dell Storage PS Series Arrays: Scalability and Growth
in Virtual Environments.
The MEM iSCSI connection algorithm works to avoid creating unnecessary sessions while still maintaining
redundancy. The Dell PS6110, PS4110, and PS-M4110 arrays have only one 10Gb Ethernet port and
therefore fewer iSCSI connections are created compared to arrays with multiple Ethernet ports per controller.
With the PS6110, PS4110, and PS-M4110 arrays in a single-member pool, MEM creates two iSCSI
connections per volume, for redundancy. In a two- or three-member pool, MEM creates a single iSCSI