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After creating a large snapshot (I assume it drifted about 30GB from the original) I noticed that vgchange -ay took noticeable longer (to the point I thought computer hanged).

What does the activation involve and why does it take so much time to activate a LVM snapshot?

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A snapshot contains the differences between the original and the "mirrored" device. For being able to use both of them, it is necessary to map these differences to the "original" device (in memory). This is the more time-consuming, the fuller the "difference device" becomes.

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    Hmm. Any idea why it is done eagerly instead of lazily or asynchronously? Commented Sep 10, 2011 at 14:07
  • No, alas - never thought about it. Maybe because it "probably" assumes to need potential access to every block?
    – glglgl
    Commented Sep 21, 2011 at 14:10

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