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JonK1
3 Argentium

What happens when one SP loses MV connectivity?

A colleague of mine asked me a question I couldn't answer properly so: let's ask the crowd!

Assume we have two VNX systems. VNX01 has LUNs that are attached to hosts. VNX02 is a replication target for all LUNs on VNX01.

Both systems replicate using MV/S. The MV ports are dedicated for this purpose.

  1. If we would reboot SPA on VNX01, all LUNs would trespass to SPB. The secondary copies on VNX02 would also trespass to SPB. Host access continues, replication traffic continues. Correct?
  2. If we flip it around: we reboot SPA on VNX02 (the secondary array). As far as I know this will not result in a trespass on the primary array. Since you can't replicate from SPA to SPB, this will cause all mirrors that run on VNX01 SPA to sysfracture. Once SPA on VNX02 comes back and depending on the "correct" Auto Recovery setting on the mirrors, replication will resume. Correct?

But what happens when I unplug the MV cable between both SPA's: will the mirrors sysfracture? Or will the primary system trespass all LUNs from SPA to SPB?

I'm very much in favor of choosing option 1 (sysfracture) since a massive amount of trespasses (depending on system load) could result in a massive performance impact on host level (as far as data unavailability) depending on system load, but I'm not sure. Does anyone have any experience on this?

Cheers!

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5 Replies
christopher_ime
4 Beryllium

Re: What happens when one SP loses MV connectivity?

Jon,

Each of these scenarios are described in detail in the MirrorView Knowledgebook.  Search for it by name on support.emc.com.

Personally not a fan of direct links in the forum as they go stale and may not reference the latest.  The latest is titled:

White Paper: MirrorView Knowledgebook: Releases 30 - 32 - A Detailed Review

Skip to the section: "MirrorView failure recovery scenarios"

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JonK1
3 Argentium

Re: What happens when one SP loses MV connectivity?

Aha, that's where it's at! I've been looking to MirrorView study resources guides all morning but couldn't find it. Thanks!

For completeness of the thread:

If the storage system containing the secondary image fails, the secondary image is system fractured. Similarly, if the link between the primary and the secondary storage system fails, the secondary image is also system fractured. In either event, once the issue has been resolved and the secondary storage system is back in communication with the primary storage system, the secondary image is automatically resynchronized if auto recovery policy is enabled.

So in case of link failure, the mirrors in question fracture.

RRR
5 Osmium

Re: What happens when one SP loses MV connectivity?

Nice! Good question and to the point answer without really having to start looking for the exact document. Nice one Jon and Christopher

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christopher_ime
4 Beryllium

Re: What happens when one SP loses MV connectivity?

Sorry, didn't mean for it to come off as RTM, but I blame the SECURED PDF and the fact that I couldn't copy and paste plus it was late.  Hehe, my devious plan of letting someone else manually type out the text and therefore the answer in the white paper had worked.  Thanks Jon; for sharing of course

JonK1
3 Argentium

Re: What happens when one SP loses MV connectivity?

Haha

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