ccd mirror vs. raidframe - BSD

This is a discussion on ccd mirror vs. raidframe - BSD ; The OBSD 3.7 ccd man page says it supports mirroring. What advantages/disadvantages does it have in comparison to raidframe in a raid1 configuration? Which is more reliable/robust? Which uses less OS resources? Which is easier to recover after a hard ...

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Thread: ccd mirror vs. raidframe

  1. ccd mirror vs. raidframe

    The OBSD 3.7 ccd man page says it supports mirroring. What
    advantages/disadvantages does it have in comparison to raidframe
    in a raid1 configuration?

    Which is more reliable/robust?

    Which uses less OS resources?

    Which is easier to recover after a hard system crash or disk failure?

    Can ccd mirror the / partition? (raidframe can but I think you can't
    boot directly onto the raid, so a separate boot partition is needed)

    The ccd driver is already included in GENERIC, but raidframe is not and
    requires a bit more work to setup. Is it worth it, or is ccd just as
    good?

    Which would you use to protect your data?...

  2. Re: ccd mirror vs. raidframe

    In article ,
    gargoyle wrote:

    > The OBSD 3.7 ccd man page says it supports mirroring. What
    > advantages/disadvantages does it have in comparison to raidframe
    > in a raid1 configuration?
    >
    > Which is more reliable/robust?
    >
    > Which uses less OS resources?
    >
    > Which is easier to recover after a hard system crash or disk failure?
    >
    > Can ccd mirror the / partition? (raidframe can but I think you can't
    > boot directly onto the raid, so a separate boot partition is needed)
    >
    > The ccd driver is already included in GENERIC, but raidframe is not and
    > requires a bit more work to setup. Is it worth it, or is ccd just as
    > good?
    >
    > Which would you use to protect your data?...


    RAID frame supports more than just striping and mirroring.
    Personally I use RAID level 5 and with a bit of work you can use that
    for / and the rest ...

    Not used ccd as until your post I wasn't aware it could do mirroring.
    also to use mirroring I'd need an additional disk (I have 3 x 200GB disk
    and that gives me 400GB of protected storage in raid 5 - for mirroring
    I'd need 4 disks).

  3. Re: ccd mirror vs. raidframe

    On 2005-05-19, Ryoko wrote:
    > RAID frame supports more than just striping and mirroring.
    > Personally I use RAID level 5 and with a bit of work you can use that
    > for / and the rest ...


    That's true, but I'm only interested in RAID-1. It's more expensive,
    but easier to deal with and that justifies the additional cost for me.

    It should also be less resource-hungry than RAID-5 since there is no
    XOR overhead, but I don't know if that makes much difference or not.

    > Not used ccd as until your post I wasn't aware it could do mirroring.
    > also to use mirroring I'd need an additional disk (I have 3 x 200GB disk
    > and that gives me 400GB of protected storage in raid 5 - for mirroring
    > I'd need 4 disks).


    Yup, it cost more. OTOH, you could lose two disks and still have a
    working system (unless both disks of the same mirror die!) Of course,
    you could make that 4th disk a hot spare for your RAID-5 and get more
    reliability that way too.

    But I like RAID-1 for the simplicity, and also because some of my
    machines simply don't have room or power for more than two disks.
    Hence, I'm using raidframe in raid1 mode now, but I'm wondering if
    there's any incentive to go with ccd mirror instead...

  4. Re: ccd mirror vs. raidframe

    gargoyle writes:

    > It should also be less resource-hungry than RAID-5 since there is no
    > XOR overhead, but I don't know if that makes much difference or not.


    The disk I/O is probably more likely to affect performance, not the
    XOR calculation (especially on today's CPU). The following paper
    describes the I/O characteristics of various RAID schemes:

    http://citeseer.ist.psu.edu/chen89evaluation.html

    The following two may also be of some interest:

    http://citeseer.ist.psu.edu/chen90maximizing.html
    http://citeseer.ist.psu.edu/219910.html

    > Yup, it cost more. OTOH, you could lose two disks and still have a
    > working system (unless both disks of the same mirror die!) Of
    > course, you could make that 4th disk a hot spare for your RAID-5 and
    > get more reliability that way too.


    Depending on your I/O characteristics and speed needs, RAID 0+1 may be
    another idea.

    --
    David Magda
    Because the innovator has for enemies all those who have done well under
    the old conditions, and lukewarm defenders in those who may do well
    under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI

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