FAQ
Hi all.

Currently I am administering a mail cluster in which messages are
stored on software RAID shared with NFS. There are several NFS
servers, every one of them exports a part of all mail files for a
specific frontend with postfix.

We are thinking about replacing these storage hosts with one solution,
maybe a storage array with appropriate disk space and I/O capacity.
What are pros and cons of that solution? Do storage arrays have
appropriate I/O capacity (X*software RAID)? Does it scale good? Does
storage capacity also scale good in those solutions?

Best regards,
R.

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  • John R Pierce at Jan 14, 2012 at 5:16 am

    On 01/14/12 1:56 AM, Rafa? Radecki wrote:
    We are thinking about replacing these storage hosts with one solution,
    maybe a storage array with appropriate disk space and I/O capacity.
    What are pros and cons of that solution? Do storage arrays have
    appropriate I/O capacity (X*software RAID)? Does it scale good? Does
    storage capacity also scale good in those solutions?
    those questions are all extremely vague. 'storage arrays' vs 'storage
    hosts' could mean almost anything. without a thorough analysis of your
    workloads, its impossible to guess what your performance or capacity
    requirements are.



    --
    john r pierce N 37, W 122
    santa cruz ca mid-left coast
  • Nicolas Thierry-Mieg at Jan 14, 2012 at 5:19 am

    John R Pierce wrote:
    On 01/14/12 1:56 AM, Rafa? Radecki wrote:
    We are thinking about replacing these storage hosts with one solution,
    maybe a storage array with appropriate disk space and I/O capacity.
    What are pros and cons of that solution? Do storage arrays have
    appropriate I/O capacity (X*software RAID)? Does it scale good? Does
    storage capacity also scale good in those solutions?
    those questions are all extremely vague. 'storage arrays' vs 'storage
    hosts' could mean almost anything.
    file a bug report on google-translate ;-)
  • Devin Reade at Jan 14, 2012 at 1:17 pm

    Rafa? Radecki wrote:

    We are thinking about replacing these storage hosts with one solution,
    maybe a storage array with appropriate disk space and I/O capacity.
    As John had mentioned the solution really depends on a complete
    analysis of your requirements (average and maximum message size,
    number of messages, number of submailboxes, number of users,
    number of concurrent users, interconnect, etc). I'm not sure if
    you're talking about replacing just the storage subsystem or the
    entire mail system, but I'll assume the latter.

    Although I mentioned Cyrus Murder
    <http://cyrusimap.web.cmu.edu/mediawiki/index.php/Cyrus_Murder>
    on the other thread, that is intended for truly large installations
    and may (or not) be overkill in your situation.

    One nice thing is that a basic Cyrus installation (without the Murder
    part of the architecture) installs onto a single host (and is
    available in the CentOS distribution), and can scale up when
    circumstances dictate. Cyrus is extremely easy on resources;
    probably a decade ago I had (going by memory) over 100,000 users on
    one machine.

    One configuration I like for "single instance" (non-Murder) installations
    is to run Cyrus in a two-node pacemaker/corosync active-passive cluster
    using DRBD and local disk as the storage. In this configuration
    both nodes have mailscanner + sendmail running (equal MX priorities
    in DNS), and both are configured to hand off the messages via
    lmtp to the active node's cyrus processes. These are sealed
    servers (no general login access) with authentication tied into
    a master-replica LDAP configuration. And of course the local storage
    on the nodes is Linux software RAID (so it's replicated at not
    only the host level but also the DRBD level).

    Even ignoring the usual HA aspects, it's nice to be able to do most
    maintenance without bringing down the mail system.

    And of course if your site is large enough that the "single instance"
    configuration runs out of capacity, you can still expand it into
    the Cyrus Murder architecture quite easily.

    With respect to NFS, trying to use it as the back end storage has
    the usual problem with NFS locking and perhaps performance. Using
    has in the past been contraindicated, but I've not looked into
    that issue recently to see if there are any changes. If you're leaning
    toward a storage appliance (netapp or whatever), I would expect
    cyrus to work just fine with iSCSI.

    Cyrus also has nice searching and mail filtering capabilities.

    Devin
  • Lisandro Grullon at Jan 15, 2012 at 12:07 am
    I hope you will be clustering those storage arrays since email is such a vital service for any organization. What are your current choices? I don't think there would be any major issues as long as you plan you current and long term capacity needs. Let us know what are your plans at the moment.

    ------Original Message------
    From: Rafa? Radecki
    Sender: centos-bounces at centos.org
    To: CentOS mailing list
    ReplyTo: CentOS mailing list
    Subject: [CentOS] Storage - posibilities?
    Sent: Jan 14, 2012 4:56 AM

    Hi all.

    Currently I am administering a mail cluster in which messages are
    stored on software RAID shared with NFS. There are several NFS
    servers, every one of them exports a part of all mail files for a
    specific frontend with postfix.

    We are thinking about replacing these storage hosts with one solution,
    maybe a storage array with appropriate disk space and I/O capacity.
    What are pros and cons of that solution? Do storage arrays have
    appropriate I/O capacity (X*software RAID)? Does it scale good? Does
    storage capacity also scale good in those solutions?

    Best regards,
    R.
    _______________________________________________
    CentOS mailing list
    CentOS at centos.org
    http://lists.centos.org/mailman/listinfo/centos

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