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After creating 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 involves any why it takes so much to activate 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? –  Maciej Piechotka Sep 10 '11 at 14:07
    
No, alas - never thought about it. Maybe because it "probably" assumes to need potential access to every block? –  glglgl Sep 21 '11 at 14:10
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