Why does my RAID 1 NAS have to "synchronize"?

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Apparently you just created the array. The copying of files has nothing to do with it. Both disks are supposed to always contain the same data, so when you first create the array, the entire contents of the first drive has to be copied to the second to ensure they are identical. After that finishes, then writing data just writes to both drives at the same time.

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jonathanwiesel
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jonathanwiesel

Updated on September 18, 2022

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  • jonathanwiesel
    jonathanwiesel over 1 year

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  • jonathanwiesel
    jonathanwiesel over 10 years
    I checked that one out also, but I'm not sure how the procedure to make a proper authenticated request is made.
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    jonathanwiesel over 10 years
    never mind, I managed to edit the library code to make it suit my needs, thank you
  • Steve Bennett
    Steve Bennett about 9 years
    But that's not what's happening. The creation (and initial synchronisation) was very fast - a few minutes. But since then, it's very slow - something like 36 hours since I first started copying 1TB on.
  • psusi
    psusi about 9 years
    @SteveBennett, there is no way the initial sync only took a few minutes for a TB+ size array. 6-18 hours maybe, not minutes.
  • Steve Bennett
    Steve Bennett about 9 years
    For empty disks? Ok. But in any case, I previously did a Time Machine backup to there, and it then slowly synced to completion. Now I copy another 1TB onto the disk, and again, a very slow sync process afterwards. Although I did inadvertently force-shutdown the NAS (sigh: 1.5 seconds on power button = soft shutdown, 5 seconds = hard), so maybe that has triggered the need for a complete resync?
  • psusi
    psusi about 9 years
    @SteveBennett, there is no such thing as empty. Disks always contain some kind of data, whether you assign any meaning to it or not. Yes, a force-shutdown would trigger a full resync, unless you have bitmaps enabled ( but they cause a slight loss of write performance )
  • Steve Bennett
    Steve Bennett about 9 years
    Ah, ok. I guess that's the actual issue here.
  • Paul-Sebastian Manole
    Paul-Sebastian Manole almost 8 years
    RAID does not know that there is no data there. It does not work at the file system level. So syncing copies the main drive(s) to the mirror drive(s) upon creating the array first time or switching to spare drive or when you changed defective drive.