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Questions regarding VMs

  • 1.  Questions regarding VMs

    Posted Mon January 25, 2021 10:58 AM
    Hello All,

    I've been working with Informix for a number of years, but always on physical servers. We now are migrating to virtual servers running under VMWare/SimpliVity. As part of this, we will be upgrading our Informix from 11.70 to 14.10, and from RH 7.x to 8.2. I understand the basics of server virtualization, but there are many variations and different capabilities, so I've got questions.

    Leaving aside the performance benefits of having local replicated copies of your databases, is there any benefit to using Informix replication to keep a disaster recovery (DR) instance up to date, vs using the hive synchronization capabilities of something like SimpliVity?

    Currently, we have physically separate boxes at our primary site, which are kept in sync with HDR, and another server several states away that is kept up to date via RSS. Our users require the local failover machine be available within an hour (easy to accomplish with HDR), and our remote DR site to be available within 6 hours, if our primary data center is lost due to fire or other disaster. Further, in the case of switching to the DR site, the users are willing to accept a loss of up to one hour's worth of work. Those requirements were put in place before we implemented the replication, and never updated to reflect the fact that we actually can come up much more quickly.

    Looking first at the case of a local failover, the team in charge of configuring the virtual servers assures us that by using synchronization between SimpliVity hives, we could avoid the overhead and maintenance chores associated with keeping a second copy of Informix running on a second VM, and instead just spin up a new VM if/when the primary node fails. That new VM would then access a set of disks kept in sync via SimpliVity hive synchronization, and the VM itself would be a backup of our primary server, so all of the Informix binaries, config files, OS configs, cron jobs, etc., would all be present, and the new VM would even have the same hostname and IP address as the failed server.

    Intellectually, I know that all of this should be feasible from a Linux point of view, but I do not know whether the SimpliVity sync can be trusted for Informix. Obviously, if we did this, when we started Informix on the new VM, it would go through its normal fast recovery process, using whatever had been written to the disks supporting the physical and logical logs. But can that VMWare/SimpliVity sync process be trusted to get that right, so that Informix would be a happy camper?

    Taking it to the next step, if we lose the primary data center and have to transition to our DR site, similar questions arise. As I understand it, SimpliVity sync only works within the local clusters of servers, so our DR site would not be able to use that solution. So would we still want to use RSS replication for that site? Given the relatively long period that we're allowed to be down, we may be able to just have a nightly level 0 archive that is transferred to the DR site, along with copies of the logical log backups taken throughout the day, and use those to restore to the point of the last logical log backup. That's what we did prior to replication, but our database has grown since then, so we'll have to test the performance of the new servers. If that is not sufficient, we could implement Continuous Log Restore, which I've used at a previous site.

    Another question involves performance, particularly I/O performance. I've heard that some hypervisors have worse performance than others in this respect, but no one has said which are good and which are bad. Obviously, since the rest of the company already uses VMWare and SimpliVity, I can't pick and choose to get the best, but I would like to know whether this combination performs well, or if there are certain configuration settings that need to be put in place to improve the I/O performance.

    I probably will come up with other questions as we move forward with this, and I'm sure that any responses here will also make me think of additional questions.

    Thank you in advance.


    Brad Day

  • 2.  RE: Questions regarding VMs

    Posted Thu February 04, 2021 10:58 AM
    Edited by John Smith Thu February 04, 2021 10:59 AM

    At my view and my modest experience feedback, here are some ideas :

    1- Always prefer native technologies : informix replication first (HDR, RSS, CLR), instead of storage replication
    2- Try to have feedbacks from similar architecture as yours with informix of course (future architecture i mean) , and especially from Simplivity editor (HPE). and hope you will have feedback here :)
    3- do the most tests you can (CPU, Network, Storage..apps), especially for tunning the virtual machines, for  informix i think dedicated resources would be better.
    4- Think about informix licensing , moving from phyiscal to virtual world :), contact IBM support to know the licensing terms with VMWARE

    Generally, i think ,  vmware is good for small/middle companies, but for big compagnies IBM PowerVM on Power Systems the best :) (don't know about the others :) )


    John Smith