Release Notes

Deploying the MEM
8 Configuring and Installing the PS Series Multipathing Extension Module for VMware vSphere and PS Series | TR1074
connection per member, resulting in creating two or three iSCSI connections per volume. This balances the
bandwidth and throughput from an individual ESXi host with that of an individual PS Series member.
Note: The vSphere 6.0 feature Virtual Volumes changes the way the iSCSI connections are made between
the host and the volumes. See section 7, Using MEM with Virtual Volumes, for details.
2.3 Deployment considerations for iSCSI login timeout
The default value of 5 seconds for iSCSI logins on vSphere ESXi is too short in some circumstances, such as
a large configuration where the number of iSCSI sessions to the array is close to the limit of 1024 per pool. If
a severe network disruption were to occur, such as the loss of a network switch, a large number of iSCSI
sessions need to be reestablished. With such a large number of logins occurring, completely processing the
logins takes longer than the five-second default timeout period. The MEM installer automatically sets the
iSCSI Login Timeout to the value of 60 seconds as recommended by Dell EMC.
The iSCSI Login Timeout value can be set using esxcli with the following syntax:
esxcli iscsi adapter param set --adapter=vmhba --key=LoginTimeout --value=60
Note: By default, the MEM setup.pl will attempt to update this value at configuration time.
2.4 Deployment considerations and best practice parameters
The MEM setup.pl script for configuring the ESXi host iSCSI vSwitch can be pass the --bestpractice
parameter, which enables the following best practices:
Disabling Delayed ACK: Delayed ACK is a TCP/IP method of reducing I/O overhead by allowing segment
acknowledgements to piggyback on each other or on other data passed over a connection. One side effect of
delayed ACK is that if the pipeline is not filled, acknowledgement of data is delayed. In SAN Headquarters
(SANHQ), this can be seen as higher latency during lower I/O periods. Latency is measured from the time the
data is sent to when the acknowledgement is received. Since we are talking about disk I/O, any increase in
latency can result in poorer performance. Additional information can be found in VMware Knowledge Base
article 1002598.
Disabling Large Receive Offload: Similar to Delayed ACK, Large Receive Offload (LRO) works by
aggregating packets into a buffer before the received data is sent to the TCP stack. With iSCSI storage, this
additional latency inserted into the process could potentially reduce performance for some workloads.
Additional information can be found in VMware Knowledge Base article 2055140.
Note: While iSCSI login timeout is considered a best practice, it is also consider a requirement, and therefore
is always set to 60 seconds during configuration.