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Problem/Questions regarding FCtool 4.3.2

  • 1.  Problem/Questions regarding FCtool 4.3.2

    Posted Thu July 09, 2020 09:19 AM
    Hi everyone

    First of all, I'm note sure if this is the right sub-forum/board/community (Storage Management doesn't exist anymore) but well, here we go.

    We recently updated from FCtool 4.2.1 to version 4.3.2 and it seems we ran into a "small" problem:

    8394    SVC::check_free_cap(2590): FCT9054T Pool      ZX_HANA_FC: capacity      9,216 GB, free      4,176 GB, used      4,738 GB,  52% Needed capacity for flashcopy:     14,336 GB

    8394    SVC::check_free_cap(2598): FCT9055T Not enough free capacity : Pool ZX_HANA_FC has free capacity of 4,176 GB, needed space is: 14,336 multiplied by STORAGE_FREE_CAP_FACTOR 10

    So far so good .... 14TB don't fit into 4TB. We then cleared the SVC pool of old snapshots ("spaceefficient backups") and expanded it to 20TB (as 14TB also wouldn't fit into 9TB). Then we tried again to create a snapshot ("spaceefficient backup") into this big and empty pool and ran basically into the same problem:

    8881    SVC::check_free_cap(2590): FCT9054T Pool      ZX_HANA_FC: capacity     20,480 GB, free     20,480 GB, used          0 GB,   0% Needed capacity for flashcopy:     14,336 GB
    8881    SVC::check_free_cap(2598): FCT9055T Not enough free capacity : Pool ZX_HANA_FC has free capacity of 20,480 GB, needed space is: 14,336 multiplied by STORAGE_FREE_CAP_FACTOR 10

    So now the whole backup of 14TB would fit into the pool (20TB free) but we still get the "not enough free capacity) error.

    So there are a couple of questions:
    - Why? (14TB do fit into 20TB)
    - the "is there enoguh free capacity in to pool" feature has been introduced in FCtool 4.3.x - is there a way to disable the check?
    - what does "multiplied by STORAGE_FREE_CAP_FACTOR 10" mean and can we change/disable it?
    - why does the "free capacity" feature check for the fully alloctable space (our HANA source disks are 14TB in total) and not the "spaceefficiant" sapce. The 4.5TB that were marked as used consisted of 2 spaceefficient backups of these 14TB disks so another spaceefficient backup would have easily fit into the remaining 4TB


    Hope you guys can help
    Peter

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    Peter Wyder
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  • 2.  RE: Problem/Questions regarding FCtool 4.3.2

    Posted Fri July 10, 2020 02:25 AM
    Hi Peter,
    that is for safety reason: The flash copies are space efficient, but if you do a restore then you need additional capacity, and some, at least one, flash copy target will become a full copy. Also remaining capacity may be needed in the future to expand existing VD, ....
    In your case: if 20 TB are remaining, one full backup would take 14 TB (not used because of space efficient), then due to cascading flash copy mappings, one single restore would not be possible, most likely. So please have an eye on your free capacity ...
    To overwrite:
    fctool --backup --special STORAGEFREECAPFACTOR=n ...
    n can be between 1 and 10
    -- Markus Fehling

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    Markus Fehling
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