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The performance of ldiskfs+LVM snapshots quickly declines when there are multiple snapshots in existence, since the block-layer snapshot requires data copies for each snapshot copy.
Rather than having a layered ldiskfs on top of a block-layer snapshot device, it would be better to have an integrated fileystem-level snapshot in ldiskfs, more similar to that of ZFS, so that snapshot blocks/inodes can be COW-referenced within the filesystem without a data copy.
It is desirable to have a whole-filesystem snapshot mechanism, unlike DL-Snap in LU-11512, which requires whole-filesystem traversal in order to make an explicit copy of every directory/file being snapshotted. That can take a considerable time for large filesystems, and multiplies metadata consumption for each additional snapshot created.
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