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joseph_gk

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joseph_gk

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January 23rd, 2013 09:00

Boot LUNs presented from VMAX

Is there a best practise w.r.t presenting thin devices from a VMAX array for boot from SAN? These thin devices will be bound to a FC pool and will be fully pre-allocated. Is it recommended to enable FAST VP on these boot LUNs? Is there any advantage in having the boot devices as thick devices (with dedicated spindles) instead of having them as preallocated Thin devices?

  • Zikas

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    Posted January 23rd, 2013 16:00

    Hi Joseph,

    from my experience i know that BOOT devices, fence devices, quorum devices it is not recommended to enable FAST VP on them, so you have to PIN them on the FC pool.

    Also the REDO logs if i remember well must be pinned to the FC pool.

    I will try to find the document that says that recommendation.

    Also from my experience there isn't any serious advantage of having the boot devices as thick instead of having them as THIN.

    Only if you are using SRDF and there is a limitation on the replication from thin to thick. I mean VMAX on the Producton and DMX on the DR Site.

    So far (it is 02:30 Greek local time) and i cannot think something else.

    Maybe later the expert will jump in the discussion and they will us their "lights".

  • Kleanthis76

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    Posted January 24th, 2013 01:00

    Hi joseph_gk,

    In addittion to what Zikas wrote, boot & swap devices do not need to be under FAST DP/VP control as long as you don't put any production data in them. Mainly boot device is read during the host boot time and the swap device has mainly writes that goes to cache first. So if you don't have any production data on boot device, boot and swap devices are usually placed under FC technology and left there (always create stripe meta for them to avoid hit the Device WP limit). Instead of pinning which is one solution you can create cascade storage groups and have one child SG with boot & swap devices and another child SG with the data devices (that you are going to place under FAST control).

    Thin provisioning is done on storage, so the host is not aware of that, unless of course you have a thin enabled LVM (like VxVM 5, Win2k8 etc). In any case preallocation is not necessary.

    Regards,

    Kl.

  • Zikas

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    Posted January 24th, 2013 03:00

    Hi Kleanthi,

    your advises and comments are very useful.

    Thank you.

  • joseph_gk

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    Posted January 24th, 2013 06:00

    Thanks for your comments. Please let me know if you come across any best practices document for the same.

    Regarding preallocation, I think EMC recommendation is to fully allocate (pre-allocate) the Thin devices which are used as boot devices. Correct me if I am wrong.