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vMSC RTT with VPLEX Metro

Hi Team, IHAC that is implementing vMSC (ESXi6.0) with VPLEX Metro 5.3 and Uniform cross-connect using VMware NMP and need to provide them with a definitive answer on the supported RTT by VMware and EMC. Unfortunately, it seems that the EMC Simple Support Matrix for VPLEX and the VMware vMSC KB ( contradict each other as follows: 1. VMWare KB:  “The maximum round trip latency on both the IP network and the inter-cluster network between the two VPLEX clusters must not exceed 5 milliseconds round-trip-time for a non-uniform access configuration and must not exceed 1 millisecond round-trip-time for a uniform host access configuration”. 2. EMC VPLEX Simple Support Matrix:  Footnote g) For VPLEX Metro 5.3 and later releases, VMware FT and VMware HA 5.5 and later can be used up to 5ms RTT for cross-connect and 10ms RTT for stretched configurations”. VMware have subsequently stated:  "I understand from your case description that you are looking for the correct  RTT recommendation for implementing vMSC with VPLEX.  I can confirm the KB article is not outdated. We recommend to have the RTT 1ms for Cross connect. RTT . Please go ahead cross verify with EMC once as we go by our article since its published after testing in our lab environment." Any help on what is actually supported would be appreciated.

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Re: vMSC RTT with VPLEX Metro


I believe the VPLEX ESSM statement reflects x-connect support for up to 5ms when PowerPath/VE is used.  PowerPath/VE has  'auto-standby' mode that will put high latency (remote) paths into standby mode.  This provides the improved performance required to work at greater RTT.  NMP, on the other hand, does not have this capability and it was determined that manually placing remote paths into standby mode is too burdensome and error-prone to maintain over time.   NMP @ 1ms works fine and is supported.  NMP @ 5ms should be avoided for performance reasons, even though it may appear to technically work without I/O errors.  What is your customers RTT latency?



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Re: vMSC RTT with VPLEX Metro

Thanks Don,

I am a little concerned because the VPLEX ESSM states that both NMP and PPVE is supported at also provides the following footnote:

Starting with VPLEX GeoSynchrony version 5.3, cross-connected hosts for Metro configurations are supported up to 5 ms RTT.

I understand the constraints with Multipathing but cant find where the RTT is limited as a result in our support statements…

Best Regards,

Michael Cooper

Advisory Systems Engineer

EMC Global Services

Level 10/11, 345 Queen Street

Brisbane, QLD, 4000


Desk: (+617) 3032-5116

Mobile (+61) 402-105-686

Twitter: @MCooperAus

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