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Thread: Clustering NE With SuSE ES9

  1. #1
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    Default Clustering NE With SuSE ES9

    We are looking at architecting a high-availability Zimbra solution, and have a preference for SuSE over RH, mostly for experiential reasons on the SuSE side (not trying to start a distro flame war...)

    Zimbra's documentation says clustering is supported only with RHEL4, yet SuSE ES9 SP3 offers support for OCFS2 and Xen, so we are thinking about an ES9 Xen cluster with a virtual EVMS iSCSI SAN (see http://www.novell.com/documentation/...a/b3uxgac.html and http://www.novell.com/linux/technica.../4622024_f.pdf)

    We obviously don't want to run an unsupported configuration, but this looks like a good way to eliminate downtimes from doing version upgrades as well as just providing higher availabilities in general.

    Comments?

    Thanks!
    Mark

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    I see a possible issue in "upgrades" : let's say you have a mailstore cluster and you put your slave node offline to upgrade it.

    While it's offline, it does not have access to mysql (neither OpenLDAP).

    So, if it's offline (with no mysql access), it can not upgrade the database schema (same goes for LDAP).

    You need to have the live node do the upgrade. So it means downtime.

    Add to this that if your primary node fails (for what ever reason) during/after the upgrade, if your slave node tries to connect to the data, there might be a consistency error (database schema not correct for the not upgraded yet Zimbra version running on the slave node).

    I'd rather be sure the slave not stays down while doing the upgrade, then upgrade it.

    I might also be totally wrong, if I am please correct me 8)

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    Quote Originally Posted by Klug View Post
    I see a possible issue in "upgrades" : let's say you have a mailstore cluster and you put your slave node offline to upgrade it.

    While it's offline, it does not have access to mysql (neither OpenLDAP).

    So, if it's offline (with no mysql access), it can not upgrade the database schema (same goes for LDAP).

    You need to have the live node do the upgrade. So it means downtime.

    Add to this that if your primary node fails (for what ever reason) during/after the upgrade, if your slave node tries to connect to the data, there might be a consistency error (database schema not correct for the not upgraded yet Zimbra version running on the slave node).

    I'd rather be sure the slave not stays down while doing the upgrade, then upgrade it.

    I might also be totally wrong, if I am please correct me 8)
    The questions you raise are of course valid. The server cluster we were contemplating also includes a MySQL Cluster and an LDAP replica. Doing round-robin updates of both (putting updates to the database and LDAP schemas aside for the moment) is relatively straightforward. See http://doc.51windows.net/mysql/?url=/MySQL/ch15s05.html for example.

    Typically you update the offline nodes first, then take the online node offline last to update it.

    If every Zimbra update includes a database tables and LDAP schemas update, then I agree that I don't see how you can avoid some downtime.

    But, if you can update the packages first (offline), and the database tables and LDAP schemas last, downtime I think would be reduced.

    It's just that, even when we schedule Zimbra updates for off-hours and let everyone know, someone always calls to complain about "the service must be down". We've already taken to installing updates only when there is a real reason to do so.

    Mark

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