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Thursday, March 12, 2009

Question About Active Data Pools

Geoffrey Huntley recently asked me what situation would an Active Data pool be useful? To be honest, I couldn't think of a good situation. Since I don't use an Active Data Pool I thought I would throw the question out to our fellow readers to get some feedback as to how you might be using ADPs. My biggest reason for not using them was the PIT restore issue. You can read my full gripe here. Basically if TSM wont utilize it when doing a PIT then what's the benefit? I'd say more than half, if not 75%, my restores are from older dates.

4 comments:

  1. Active data pools come into their own when restoring an entire client - if you're using a file device class. That way, you can restore without needing a vast number of tape drives. Great for single server DR, or if your device class is replicated by SAN/NAS then you've got it there at the DR site already. Reduces RTO dramatically.

    Of course, if you have all the client's data in a disk pool including older versions, there's no benefit at all but who has that kind of disk storage available?

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  2. Hi Chad,

    IMOH it shouldn’t be an issue that you can't use PIT restore when the data is stored across different stgpools (aka PIT cannot be used when an ADP is used).
    You'll want to use an ADP only to collocate active files versions to a single stgpool. PIT is not needed for that, as you don't need 'historical' data seen from that perspective.

    ADP's on disk can be used for fast client restore and will reduce required resources. You don't need to hold active/inactive data on the same stgpool (or underlying tiered storage). You can keep active data on ADP (fast/expensive disk) and have the inactive data on lower cost disk/tape. ADP's on disk will give you the most advantages.

    In addition, you can create a list for nodes that will benefit from the advantages of ADP; being filesystems with small files. Create a list of nodes that require a fast restore of typically the last backup version (the active one). This way, you can leave the large databases, etc. out of the ADP.

    Another argument is that DRM don't manage ADP's. That is correct. You can use your ADP for local disasters (disk failure, clients' system down, etc.). Use simultaneous writes/copypool tapes to provide offsite DR.

    I think there a some advantages, for some people in certain environments, that can benefit from an active data pool.

    Best regards,
    Tommy Hueber
    http://www.tsmblog.org

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  3. My problem is that I rarely restore from the most recent backup. Usually its to a specific date. Sure, I'll restore individual files or folders from the most recent backup periodically, but when a system needs to be restored we usually don't do it from the most recent backup, usually its a day or so off and only the app tends to be rolled forward to the most current time. So even then is it worth the waste of space to have an ADP?

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  4. One of the great things about TSM is that there's a pile of features - but each one needs to be evaluated for its usefulness to the situation at hand. It seems in your case ADPs have no use, but maybe the de-dup features in TSM 6 will be of use to you where you can store more on the same disk pool. Many won't get much out of de-dup because they don't have enough disk to store more than a night's backup anyway.

    For getting a fast restore from previous versions, seems to me that collocation and/or a massive disk pool with many versions stored is the way to go. TSM v6 makes that a more realistic option for many but might take a while before people choose to make the move. For copy pool data, collocation in one form or another is the only way to get a full restore without tons of tape mounts.

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