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LVM 2 snapshots works as COW. However the block may change even if it is not used anymore. As SSD disks may need marking of free/used blocks to better manage blocks, the API was introduced into Linux to mark free/used blocks.

My question is - does LVM use this API? I.e. are blocks are copied on every change or only if filesystem cares about contents?

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Do you have any pointers to information about this new API? – Mark Wagner Aug 9 '10 at 23:14
Pretty sure he's referring to discard/TRIM support: – James Aug 10 '10 at 8:46
up vote 1 down vote accepted

Blocks are copied on every change.

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