SUMMARY: switch/hub for 3 T3 Raid devices

From: Shin (shin_at_solarider.org)
Date: 04/01/04

  • Next message: Shin: "SUMMARY What use are LUNs" 
    Date: Thu, 1 Apr 2004 11:54:27 +0100
To: sunmanagers@sunmanagers.org

    Apologies for the delayed summary posting.

    Once again many thanks to all who replies. Original question follows
    then the replies.

    Thanks to all,
    Shin

    On Sun, Mar 21, 2004 at 09:16:00PM +0000, Shin wrote:
    >
    > I shall be investing in 3 T3 raid arrays. I have an FC-AL card in a
    > host and I want to use all 3 devices on the same host. As they are
    > FC devices I as assuming that I can just plug all the devices into a
    > fibre switch or hub and that I should see all as seperate disk
    > devices.
    >
    > Is this assumption correct and what sort of switch/hub is
    > recommended. Are there seperate hub and switch type solutions and is
    > a there a significant difference in performance between the hub and
    > switch type solutions.
    >
    > Cost is quite important as well; if possible some details on
    > approximate cost (local currency is fine - I'll translate) and your
    > recommended devices would be handy.
    >
    > Assuming I can see all 3 as seperate disks, I will do a raid 5 setup
    > with 1 hot spare on each T3; I'm lead to believe this is the default
    > setup. How does one do LUN/Raid type setups on a T3 - is Raid
    > Manager required? Also is the default setup on a T3 to have 1 LUN?
    > If so then I will do one big filesystem on each LUN to get 3 big
    > filesystems; one on each T3.
    >
    > Does that make sense?

    ----------------------------------------------------------------
    From: Ben Rockwood

    Shin wrote:

    >I shall be investing in 3 T3 raid arrays. I have an FC-AL card in a
    >host and I want to use all 3 devices on the same host. As they are
    >FC devices I as assuming that I can just plug all the devices into a
    >fibre switch or hub and that I should see all as seperate disk
    >devices.

    Fibre Channel Arbitrated Loop. Yes you can use 3 methods:

    1) Loop from one array to another from the host to each array. The
    T3's are useful here because you can link the controllers for each
    array together and control diffrent arrays from 1 T3, rather than
    having to treat each T3 as a seperate array.

    2) Hub. Sun commonly uses Vixel FC-AL Hubs. You can find 'em on
    Ebay.

    3) Switch. Brocade is most popular. Switches are actually for
    Fibre Channel Fabrics rather than FC-AL, but you can manage FC-AL
    devices on a fabric with little trouble. Trouble here is that
    switches are pretty smart, you need to learn alot just to manage the
    switches (think of the diffrence between a NetGear Ethernet Hub
    versus a Foundry Core Switch, or a Cisco Router, there is alot more
    management involved) and you'll need to have a Fabric HBA in your
    system for a switch instead of an FC-AL HBA.

    >Is this assumption correct and what sort of switch/hub is
    >recommended. Are there seperate hub and switch type solutions and is
    >a there a significant difference in performance between the hub and
    >switch type solutions.

    Switches are obviously faster because like Ethernet your connecting
    2 devices together rather than linking all of them, but in FC-AL
    your already forming a ring topology and looping them all together
    like a token ring. So the performance speeds depend on how your
    switch is faking out FC-AL devices to make them think they are on a
    FC-AL loop rather than a Fabric.

    >Cost is quite important as well; if possible some details on
    >approximate cost (local currency is fine - I'll translate) and your
    >recommended devices would be handy.

    Switches are expensive. Hands down. Fibre Channel is expensive as it
    is, but a switch will run you $3000
    or more.

    >Assuming I can see all 3 as seperate disks, I will do a raid 5 setup
    >with 1 hot spare on each T3; I'm lead to believe this is the default
    >setup. How does one do LUN/Raid type setups on a T3 - is Raid
    >Manager required? Also is the default setup on a T3 to have 1 LUN?
    >If so then I will do one big filesystem on each LUN to get 3 big
    >filesystems; one on each T3.

    Ya, I think RAID Manager works for T3's as well. You can also log
    into the array directly and manage it that way, although it's more
    work.

    As for the rest of that paragraph, it's all dependant on what you
    want to do. You might want 3 filesystems on 3 diffrent T3's. You
    might want 1 big filesystem using all 3 arrays (using DiskSuite or
    VxVM). It's all dependant on what you want/need.
    ================================================================

    ----------------------------------------------------------------
    From: Tim Chipman

    Hi,

    To be quite honest, if you are remotely concerned about cost, then
    investing in T3's should not be on your list of options, unless the
    local sun reseller is giving you very(!!!) agressive pricing. We bought
    a T3 here 2 years ago, at "75% off list price" and even then, I'm only
    barely satisfied that it was an "acceptible price" (ie, NOT a great deal
    even at this "large discount"). Since then, T3s have not changed in
    terms of features/performance, while the storage market continues to
    move. IMHO T3 is rather dated technology and you can almost certainly
    get better value from other vendors, in terms of price:performance yield.

    Second point, is that the world of "SAN" (storage area network),
    fibre-based connectivity for disk-arrays to host(s) ... is not a place
    of "budget-concious consumers". Expect to spend a premium (!!!) for SAN
    infrastructure, plus of course $$ for training people to install and
    maintain the gear.

    Given the type of questions you are asking below, I think you are
    needing to do a bit more research about SAN in general, to better
    understand why it is a good solution in some environments, vs
    environments where it is a TERRIBLE solution. I would recommend you
    ensure your own requirements are well defined also (not in terms of "we
    need 3 T3 disk arrays" but rather, "we need X gigs / TB's of storage
    with 'this much' redundancy, 'This kind' of performance profile,
    connectivity to 'X' hosts, automatic failover/manual failover/no
    failover // easy management for rapidly changing requiremnts // no
    management since non-changing requirements ... etc etc etc".)

    IF your environment is relatively straightforward, you might be better
    off with simpler "direct attached SCSI" disk arrays. It is possible to
    purchase such arrays which may have multiple hosts attached to each
    array, giving similar functionality as that of a small-scale SAN, but
    without any added complexity of SAN (Hub/Switch connectivity, new
    equipment to learn how to administer).

    Good luck / hope this helps,
    ================================================================

    ----------------------------------------------------------------
    From: Johan Hartzenberg

    If all your devices support "fabric mode", then you /want/ a switch.
    If all your devices support /only/ loop mode, then you have to use a
    hub.

    Some switches allow you to plug loops into their ports. In my
    experience, this is looking for trouble (mixing fabric and loop
    mode)

    Switch -> Fabric
    Hub -> Loop

    The disk array and the HBA (Host bus adaptor) must support the same
    topology (Fabric or loop mode - otherwise, if you mix topologies you
    will run into interesting issues)
    ================================================================
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