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Thread: SSD cache and failover

  1. #1

    Default SSD cache and failover


    Let say i have 2 Open-E storage servers - master and slave, they will be active-passive Synchronous replicated HA enabled. The master will have Raid card with SSD caching. The slave will have software raid.
    The master storage raid card SSD cache will cache the most frequent used files. It will works as READ and Write cache.
    What happen with write cache when the main storage goes offline and the slave takeover the master's function and then after few hours master comes back online.

    What will happen with cache data if it didn't got time to flush it to main storage ? It will get corrupted ?

    The point is: Is it stupid to use write cache with Synchronous replication in order to bypass data corruption or data mismatch in both nodes in case if something goes wrong with master and its goes offline for 2 days? For sure, the new data will be written in slave in those 2 days.

    I would like to hear your thoughts about that stuff. I hope you guys understand i'm trying to say.


    //Sorry for my bad English.

  2. #2


    The caching from the controller will be independent of the iSCSI Failover.

    So if the Primary fails then all the data is now being written to the Secondary/Active server.
    When the Primary is back online then you will need to Sync the data from the Secondary/Active server then when all the volumes are Consistent then you click on the Failback button the Secondary to make the Primary Active again and all the data will be updated.
    All the best,

    Todd Maxwell

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  3. #3


    I think what RONIS want to say.

    Let's say that primary storage gone off-line suddenly (power outage, UPS failure...).
    Content of RAID write cache is safe since there is BBU installed.
    But, the content of RAID write cache still isn't written to HDDs.
    Content of HDDs (on primary storage) is synchro replicated to HDDs on secondary storage.
    But, in that moment, HDD on primary storage has data which still isn't updated because updated data still resides on RAID write cache.
    And, secondary storage will not have updated data when it take over and become active storage.

    This is serious question, and need an answer

  4. #4


    And yes,, as stated before that when the Primary regardless of the controller during that time when the server is offline the secondary is now active and writes will be on the this server until you sync'd back to the Primary. This is due to the setup of the Auto Failover service.
    All the best,

    Todd Maxwell

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    Facebook | Twitter | YouTube

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