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Aspects of mirroring
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Thread: Aspects of mirroring

  1. #1
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    Aspects of mirroring

    Hi,

    I like to know a few facts about the mirroring function of our NAS. As it takes a mere 6 hours to (re)mirror an external 250GB drive, it would be nice to know beforehand what is going to happen if you do this or that.
    1 - Can you mirror the internal drive with one that is smaller?
    2 - If I take a mirror from the NAS, with savely remove, what happens if I attach the mirror after that (if I did not change anything on the mirror)? Does this take another 6 hours or not?
    3 - The same question, but now I have changed some files. Will these changes go to the inner drive, or are they wiped out? Does this takes 6 hours or not?
    4 - Can you have different shares on one of them?

    Well, anyone who has some experience with detaching and (re)attaching is kindly asked to utter his knowledge.

    Greetz, Marc

  2. #2
    1: i have an 120gig usb-disc. And that wasnt enough. It showed a dialog with a warning message, after that it stopped the action.

    Sollie.

  3. #3
    Quote Originally Posted by mumsoft View Post
    I like to know a few facts about the mirroring function of our NAS. As it takes a mere 6 hours to (re)mirror an external 250GB drive, it would be nice to know beforehand what is going to happen if you do this or that.
    1 - Can you mirror the internal drive with one that is smaller?
    2 - If I take a mirror from the NAS, with savely remove, what happens if I attach the mirror after that (if I did not change anything on the mirror)? Does this take another 6 hours or not?
    3 - The same question, but now I have changed some files. Will these changes go to the inner drive, or are they wiped out? Does this takes 6 hours or not?
    4 - Can you have different shares on one of them?
    In my setup, I have a 300G external drive mirroring the 160G internal drive with the balance of 140G mounted as an additional volume.

    Regarding your specific questions:

    1) No. The mirror drive must be the same size or larger.

    2) Yes, if you booted the router with the external drive removed. The internal volume will be marked as "newer". This will force a resync of the internal HDD to the external HDD when the mirror is reattached.

    3) The "newest" volume wins. Unless you do something extraordinary, this is always the internal HDD.

    4) If the external HDD is larger than the internal HDD, another volume(s) can occupy the difference.

    I don't know if you are aware of this or not, but the router is still 100% usable while the raid mirror is being rebuilt. You won't have to wait for it to complete.

    Also, as part of my testing, I simulated an internal HDD failure. During this test, I was unable to use the external drive to rebuild the array via the web interface. However, I was able to mount the mirror and copy the contents to the internal HDD manually.

    - K.C.

  4. #4
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    Quote Originally Posted by kfurge View Post
    I don't know if you are aware of this or not, but the router is still 100% usable while the raid mirror is being rebuilt. You won't have to wait for it to complete.

    - K.C.
    Thanks for you answer. I'm currently busy with ripping my over 1000 CD's to the NAS, and would *hate* to loose my effort. I have had a very bad experience with loosing all the data just by mirroring it, putting the thing off without removing the external disk, and then the next morning, I removed the mirror savely, and so lost all data on the internal disk (!?!)
    I don't want to experience something like that again, hence my questions.

    What do you think, if the router rebuilds the mirror, does it overwrite all there is, or does it do something more efficient, as comparing an adding/removing? I guess not...

    Marc

  5. #5
    Quote Originally Posted by mumsoft View Post
    T I have had a very bad experience with loosing all the data just by mirroring it, putting the thing off without removing the external disk, and then the next morning, I removed the mirror savely, and so lost all data on the internal disk (!?!)
    Wow! I've performed all combinations of on/off, with/without mirror, and clean/unclean shutdowns and have never had a problem. I don't do anything special when I remove the external mirror segment. I simply turn off the router via the front power button, then unplug the drive once the router powers down. If I plug the external drive back in after a power cycle, the plex gets rebuilt automatically once the drive is detected.

    FWIW, the mirroring capability is not anything Asus did. It's part of the standard Linux kernel. That means it should be generally more reliable than other parts of the router.


    Quote Originally Posted by mumsoft View Post
    What do you think, if the router rebuilds the mirror, does it overwrite all there is, or does it do something more efficient
    It's not efficient... ;-)

    - K.C.

  6. #6
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    Quote Originally Posted by kfurge View Post
    I don't do anything special when I remove the external mirror segment. I simply turn off the router via the front power button, then unplug the drive once the router powers down. If I plug the external drive back in after a power cycle, the plex gets rebuilt automatically once the drive is detected.
    - K.C.
    Good to hear your better experience. My bad experience with about the same handling came when building the mirror for the very first time. Maybe that counts.
    Nevertheless, before I try again, I will surely copy my music via the NFS-share.

    Thanks,
    Marc

  7. #7
    Join Date
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    Angry No mirrors possible?

    After all my sorrow with the first build of a mirror I had to restore the factory defaults and re-image before MYVOLUME1 showed up again.
    I have used the Asus since then intensively.
    Now I have another go, deleted and created/formatted a foreign disk. But the Asus refuses to build the mirror this time:

    Add Mirrors/Spares Result

    OPERATION FAILED!

    Error while adding mirrors to pool `MYVOLUME1': Failed trying to add mirrors to pool.

    ??? What pool, where, why?
    I tried this 3 times with the same result. The message pops up very quickly after confirming to create the mirror
    Hope someone knows what to do next...

    Greets,
    Marc

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