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The LVM howto https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html says "In LVM2, snapshots are read/write by
by pm215 3y ago
The LVM howto https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html says "In LVM2, snapshots are read/write by default". And RedHat's docs https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_logical_volumes/snapshot-of-logical-volumes_configuring-and-managing-logical-volumes https://access.redhat.com/documentation/en-us/red_hat_enterp... include text "Since the snapshot is read/write".
So I think LVM2 snapshots are indeed read/write. Perhaps that manpage sentence was not updated since LVM1 read-only snapshots ?
(I agree with you that 'snapshot' to me strongly suggests read/write; I'm just saying that you can't actually rely on that assumption because it's not just bcachefs that doesn't use that meaning.)
- yrro 3y agoThe man page continues: > This option can create a COW (copy on write) snapshot, or a thin snapshot (in a thin pool.) [...] COW snapshots are created when a size is specified. The size is allocated from space in the VG, and is the amount of space that can be used for saving COW blocks as writes occur to the origin or snapshot. Likely snapshots _were_ originally read-only, and the description of creating thin and COW snapshots was added later, but the man page text was not re-written completely; rather the description of thin and COW snapshots were added to the end of the existing text.
- pm215 3y agoI've just noticed that I wrote "I agree with you that 'snapshot' to me strongly suggests read/write" and of course I meant "read only"! Hope that wasn't too confusing...