Hi All,
Sorry for not updating this earlier, been a bit manic.
This is the reply I had back from a senior engineer at Dell.
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The behaviour you are seeing can be expected when you set up the Multipathing Extension Module for ESX. By default, MEM will only establish 2 sessions per volume slice, & also has options for the maximum number of sessions per volume. The number of sessions for a given scenario are detailed in Table 6 on page 15 of the user guide.
The preferred method of configuring the MEM is through the esxcli command interface. An example of this which changes the number of sessions per volume to 3 can be seen on page 18 of the user guide (detailed below):
$ esxcli equallogic param set -n=VolumeSessions -v=3
It is also worth noting that in a single member group, or a group that presents an odd number if physical iSCSI ports, the sessions may not be balanced as "perfectly" as one would expect. This is because the load balancer is always striving to negotiate a better connection than the one it already has (since connection quality will change depending on the load on a given path). Sometimes, the only two sessions for a volume will come to port eth0 of a single member group. This is not a problem since, if the sessions die, & the fabric is redundant, connections into port eth1 should be milliseconds away.
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My Reply: (Based on my environemnt)
Just to confirm, this behaviour is completely normal.
With regards to the sessions established in terms of Volume sessions, would it be best practice or beneficial to set this to 3? Below shows our info
Name Value Max Min Description
--------------- ----- ----- --- ---------------------------------------------
TotalSessions 512 1024 64 Max number of sessions per host.
VolumeSessions 6 12 1 Max number of sessions per volume.
MemberSessions 2 4 1 Max number of sessions per member per volume.
MinAdapterSpeed 1000 10000 10 Minimum adapter speed for iSCSI multipathing.
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Would it be possible to please send me the guide as I have so many guides and yet I cannot find the info you mentioned on those pages (presuming I have the wrong one)
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Reply from Dell:
I can confirm that the behaviour is normal. Increasing the number of sessions from the default is beneficial in most cases, but this benefit is more noticeable when there are several hosts connecting, rather than just one. You may also want to think about aggregating the virtual network links through physical network cards. In any event, you should benchmark throughput to volumes both before & after any modifications.
The user guide for the MEM can be found here: https://support.equallogic.com/support/download_file.aspx?id=947. You can also get guides & white papers on VMware integration for various scenarios, as well as other subjects from our support site here: https://support.equallogic.com/support/tech_reports.aspx. In particular, I recommend that you look at the network performance tuning guidelines.
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These were my sessions that were established (based on my previouse reply aboce)
Reply from Dell with more explination on the above:
I just tried calling you but only got your voicemail. I wanted to clarify what you are seeing in the screenshot below. The VolumeSessions count shows the minimum & maximum possible setting for the connections to the volume as a whole, along with the current configured value. The MemberSessions count shows the same thing for the connections to a volume per member. This takes into account that a volume may be spread across more than one system in the case of a multi-member group.
In your case, you only have one member in your group, so the MemberSessions count will take precedence. You should note that the value heading is the current set limit, not the current amount of connections you should expect. The number of sessions will automatically adjust to the limits you configure as needed.
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Bit of a lost post but i hope this helps and sheds some light for others that may experience this.