[all variants] How long is mdadm --grow critical?

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http://ubuntuforums.org – Hello, I'm currently growing my software RAID 5 set with an extra drive, going from 4 to 5 drives (I'm using mdadm --grow). I've done this before and always unmounted the filesystem, just to be on the safe side. However, I have no idea what the risks are if I would use the filesystem while growing. I've read on several places that the initial part of growing is critical (presumably the 128K part?), but it's not clear to me how much risk is involved in the next part. For instance: if a drive would fail right now (during the grow), would I loose my full RAID? Or does it function right now as a (Hardware)