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Informix recommended setup for storage

  • 1.  Informix recommended setup for storage

    IBM Champion
    Posted Thu September 08, 2022 08:36 AM
    Hi everybody,

    we are planning a new database server (pair, should be HDR) for a huge customer.
    Our admins started a discussion on how to configure storage.

    We want to have ~6TB of space and are planning to be running with a set of NVME Raid (Raid 10,
    5 disks e.g. 5x3.8TB like Samsung PM9a3), alternatively multiple sets each 5 disks 1.92 TB (4+1) with two separate
    controllers or one multi-controller.
    (plus a raid 1 for OS (Linux)) Informix will be 14.10, running on iron, no virtualization.
    Database is for OLTP, huge number of tables (~1000, lots of unused tables but some very huge ones)

    On the old machine, indexes are not separated and physdbs/logdbs are on the same lvm volume (on the same devices).
    We have got PM1643 SAS SSDs there, which are already quite fast, but the new ones would be significantly faster (factor 3).


    For the db layout, the following spaces are planned
    1. relatively small rootdbs
    2. separate physlog
    3. separate logical log
    4. 2 tmpdbs
    5. huge datadbs
    6. medium indexdbs
    7. everything as raw device without filesystem 
    Typically, we would put the storage into a logical volume setup and partition it with lvs.
    Now a huge customer has a significant load in compared to others, and we want to 
    set up a machine which is configured in a more optimized way to make use of the NVME SDDs.

    Now what would be your recommendation (since positioning time of heads is not any more relevant) 
    how to configure the hardware and how to assign the partitions of the db spaces.

    Since we cannot add a separate controller per dbspace, we need to take the decision where to put what type
    of data.
    I cannot see any benefit in configuring multiple raidsets on the same disks.
    Instead I would always configure one raid set and partition it with lvm.
    Does it make sense to have two separate raid sets, keeping indexes separated from data ?
    This might be one of the bottlenecks on the old machine.
    Would splitting the indexes from data on the same raid even make a difference (because Informix
    would be able to read with a separate file descriptor) ? Or will the real effect take place only when these are moved 
    on a separate raid set / controller ?

    Does it make more sense to separate the physdbs/logdbs from the others on a separate raid set ?
    Is there a benefit from small number of bigger chunks vs. bigger number of smaller chunks ?
    Distributing chunks for the same dbs over different raid sets ?
    Tmpdbs on separate raid sets ? We do not have heavy use of tmpds now. Or can we put these on the same volume as physdbs/logdbs/rootdbs ?
    Should we try to move to more raid sets (go for 3 raids with 1,92 TB 4+1 disks instead) and distribute the load over these ?
    In terms of cache on the controllers this might be beneficial. (we need to see what would be the extra costs for this action).
    Does it make sense to make one huge raid set with 10+2 disks instead of 2x4+1 disks (because the overall 
    performance of the I/O with 10 active SSD would outperform the 2x4 active SSD ?

    What is your experience in terms of I/O bottlenecks and how to get around ?
    Today, we are sometimes suffering (on the old hardware) from slow queries. Checkpoints are ~1-2 sec, sometimes
    we have waits. 

    Maybe you can share your experience so we can take the best decision for a new machine.
    (Of course there is a budget, we need to meet ...)

    MARCUS HAARMANN


    #Informix


  • 2.  RE: Informix recommended setup for storage

    Posted Sun September 11, 2022 05:03 AM
    Marcus

    This PDF presentation authored by @Lester Knutsen  answers many of the questions you have posed...

    ​https://advancedatatools.com/wp-content/uploads/2020/03/Informix_Tutorials-Managing_Informix_Disk_space.pdf

    ...Have a perusal. There is information in there specific to dbspace organisation which may be of interest.

    ------------------------------
    Kirit Rana
    ------------------------------