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Thread: When will software RAID hotswap work?

  1. #1

    Question When will software RAID hotswap work?

    So, when will software RAID hotswap work? Or, is it just one of those things that is just infeasible?

    We'd like to use this for our lower-end boxes (1U, 4 hard drive), so we don't have to waste money or slots with a raid controller. At this low end, software raid and hardware raid are pretty close in performance (not counting controller cache), and one of the boxes we use has a special connector that hooks up from the hot-swap back-plane to the motherboard, so it'd be kind of a pain to have to get another kind of cable to hook up to a hardware raid controller.

  2. #2

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    We dont have any plans for this as I believe it is hardware related.
    All the best,

    Todd Maxwell


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  3. #3

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    In linux, it is possible to do a software raid hot-swap without rebooting or making the array unavailable, but you have to do it manually (i.e. log in as an administrator and run some commands). This is fine and preferable if you only have 4 drives (with no hot spare), where you're going to manually add a drive anyways. Perhaps this can be added to the mile-long list of feature requests?

  4. #4

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    I believe there's a kernel patch that supports hot-plugging and "warm-plugging" (whatever the heck that means). It's called libata. I guess I'll just have to wait until it's included in the mainstream kernel.

    http://ubuntuforums.org/archive/index.php/t-239597.html

  5. #5

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    Hmmm... Maybe hot-plugging/swapping IS supported under the mainline kernel? I haven't tried yet with the new version of Open-E. I'll try it out and tell you if it works. Who knows? Perhaps the new kernel version will allow it to "Just Work (R)."

  6. #6

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    Here's a link to someone who seems to be entirely satisfied with hot-swapping and software RAID under linux:
    http://www.earth.li/~noodles/blog/20...-on-linux.html

  7. #7

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    Thanks for the research - I will forward to our engineers. Hopefully we can do this. Please give us time as we are booked with request.
    All the best,

    Todd Maxwell


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  8. #8

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    You're welcome, Todd.

    Heh, no dice. I have 3 drives plugged in, which DSS sees. If I unplug one of them and do a system rescan, for some reason it only sees ONE drive (the middle one, if you're curious). If I reboot so that I only have two drives and then plug the third one in and do a rescan, for some reason it still only sees ONE drive (oddly). So, I guess I would highly recommend only plugging in and unplugging drives once the system is OFF if you're using the software RAID.

    Someday, though...

    (Robust software raid support would be great so that someday I can combine lots of iscsi volumes into one big volume using the iscsi initiator built-in to DSS. There are probably better ways to do this, though.)

  9. #9

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    I meant "unit rescan," not "system rescan."

  10. #10

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    After looking at this again, I realized that I hadn't set the BIOS to set up the sata drives as AHCI. I think they were set up to look like IDE drives or something like that. Anyways, AHCI supports hotswap, whereas regular IDE drives do not, so there's still a good chance that hotplugging could work once I set the BIOS properly on Monday.

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