SIOC is fully supported by SRM 5…er…except for planned migrations!


I was having some issues with SIOC and SRM 5 Planned Migrations. I noticed that my planned migration were failing when SIOC was enabled.

This got me thinking to whether SIOC is even supported with SRM 5, but I couldn’t even find documentation online whether it was supported. Looks like any mention of it has been omitted from the official documentation.

So after a bit of digging here is what I’ve found from VMware:

1) SIOC is supported for use with SRM – you can use SRM to protect SIOC enabled datastores

2) to execute a “planned migration” with SRM – you will need to disable SIOC first (on the datastores). You can not do a “planned migration” with SIOC enabled.

Lets start with the good news — SIOC is supported by SRM 5, so you can leave it enabled on all your replicated datastores.

This leads us to Point 2 – There are a few caveats:

As per KB2004605, you cannot unmount a datastore with SIOC enabled. If you are going to initiate a Planned Migration, you need to disable SIOC first on your protected site (active) LUNS. This is because SRM needs to unmount the active LUNS before it breaks the mirror and sets the read-only LUNS in your Recovery Site to read-write and mounts them on all ESXi hosts.

If you attempt a Planned Migration without disabling SIOC, the unmounting of LUNS and therefore the Planned Migration will fail.

There are other instances where a mounted datastore would need to be unmounted. Consider the following scenario, I haven’t had a chance to test this, but this is what I think will happen:

  1. For whatever reason your protected site (DC1) goes offline.
  2. Login to SRM at your Recovery Site (DC2) and initiate your Disaster Recovery plan
  3. The Protected (DC1) site array is unavailable so SRM is unable to synchronise changes, but it continues the recovery –
  4. SRM Instructs RecoverPoint\SRDF to break the mirror and convert the read-only recovery site (DC2) LUNS to read-write and SRM mounts them in vCenter.
  5. SRM powers on your VMs. Job done!
  6. But wait, the old protected site (DC1) eventually comes back online.
  7. You login back in SRM and hit Reprotect to start replicating back the other way
  8. SRM tries to unmount the LUNS in vCenter in DC1 before it begins replication back the other way but cannot because SIOC is enabled.
  9. The reprotection fails.

It seems clumsy to me that SRM isn’t aware of SIOC – It doesn’t matter whether it’s during a planned migration or a re-protect, if you have to keep disabling and re-enabling it’s a pain in the arse.

Clearly this isn’t going to happen a lot once you go live and its an annoyance at best, but this is the sort of minor issue that a polished product like SRM 5 shouldn’t have. Maybe I’m being so critical because it is such a good product now – they’ve raised my expectations!

I’ve raised a feature request with VMware to have this automated in a next release and I’ve been told the documentation will be updated to ‘state the obvious’.

Maybe I am blissfully ignorant of the complexity involved but as an enterprise end user it looks like a gap to me that needs fixing.

Manual steps introduce uncertainty and risk and this looks like an issue that should be solved.

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2 responses to “SIOC is fully supported by SRM 5…er…except for planned migrations!

  1. Pingback: vIrtuaLization IL » Blog Archive » SRM 5, Planned Migration ו-SIOC

  2. Pingback: Technology Short Take #24 - blog.scottlowe.org - The weblog of an IT pro specializing in virtualization, storage, and servers

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