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Trusting TrueCopy

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For those people who use TrueCopy on a daily basis, you’ll know that the assignment of a TrueCopy pair is based on a source and target storage port, host storage domain and LUN. This means a LUN has to be assigned out to replicate it.

The part that has always worried me is the fact that the target LUN does not need to be in a read-only status and can be read-write.

Please, HDS to save my sweaty palms, change the requirement to make the target volume read-only before it can be a TrueCopy target….

About Chris M Evans

Chris M Evans has worked in the technology industry since 1987, starting as a systems programmer on the IBM mainframe platform, while retaining an interest in storage. After working abroad, he co-founded an Internet-based music distribution company during the .com era, returning to consultancy in the new millennium. In 2009 Chris co-founded Langton Blue Ltd (www.langtonblue.com), a boutique consultancy firm focused on delivering business benefit through efficient technology deployments. Chris writes a popular blog at http://blog.architecting.it, attends many conferences and invitation-only events and can be found providing regular industry contributions through Twitter (@chrismevans) and other social media outlets.
  • krion

    BTW, TC pair can be based on LDEV number, without defining port, host and LUN number.

  • aDEPT

    Have you ever tried writing to the target LUN? From memory, if the copy status is “PAIR” then the S-VOL is read-only. If you go into PSUS mode, then you can write to the S-VOL, but the pairresync operation (COPY state) will copy over blocks modified on the P-VOL and those you have modified on the S-VOL.

    I can’t rememebr which document it is in, but there is a table in one of the HDS documents that explains what you can do to the P-VOL and -SVOL in each ofthe different tru-copy states. It may have been teh CCI reference guide.

  • Chris M Evans

    Yes, I was describing the initial process of creating a pair. I agree once a pair is established, then the S-VOL is read/only but not until then!

    Krion, are you referring to creating the pair with CCI? Storage Navigator currently doesn’t allow this option – although I will double check CCI.

  • snig

    CCI definitely lets you use LDEVs now. I wish SN did the same.

    I’m not so sure of the need for the read only before creating the pair. Unless maybe you’re running production on the remote system.

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