Add zfs-verify documentation to readme.md

README.md

@@ -70,6 +70,60 @@ bash zfs-move-over-ssh.sh \
   tank admin@new-server backup/tank
 ```
 
+## Verification
+
+`zfs-verify-over-ssh.sh` compares each ZFS filesystem below `SOURCE_POOL` to
+the corresponding filesystem below `DESTINATION_ROOT`. For example,
+`tank/data/documents` is compared with `backup/tank/data/documents`.
+
+```bash
+bash zfs-verify-over-ssh.sh [options] SOURCE_POOL REMOTE_HOST DESTINATION_ROOT
+```
+
+Both sides of every filesystem pair must be mounted. The transfer script uses
+`zfs receive -u`, so mount the received remote datasets before verification:
+
+```bash
+ssh admin@new-server 'sudo zfs mount -a'
+bash zfs-verify-over-ssh.sh tank admin@new-server backup/tank
+```
+
+The verifier uses `rsync` with `--dry-run`, `--checksum`, `--delete`, archive
+metadata preservation, hard-link checking, ACL checking, extended-attribute
+checking, and `--one-file-system`. It does not modify either host. Any
+itemized `rsync` output identifies an extra, missing, changed, or
+metadata-different path.
+
+Verification options:
+
+| Option | Description |
+| --- | --- |
+| `-i`, `--identity-file FILE` | Use the specified SSH private key. |
+| `-p`, `--ssh-port PORT` | Connect to the specified SSH port. |
+| `-h`, `--help` | Show command help. |
+
+Use the same key and port options as the transfer when required:
+
+```bash
+bash zfs-verify-over-ssh.sh \
+  --identity-file ~/.ssh/zfs-migration \
+  --ssh-port 2222 \
+  tank admin@new-server backup/tank
+```
+
+Exit statuses:
+
+| Status | Meaning |
+| --- | --- |
+| `0` | All checked filesystems are identical. |
+| `1` | One or more filesystem pairs have differences. |
+| `2` | Verification could not run, for example because of missing commands, SSH or sudo access, unavailable datasets, or unmounted filesystems. |
+
+For a stable result, stop writes to the source and destination while the
+verifier runs, or verify mounted clones of the same snapshots. The verifier
+checks file content and selected filesystem metadata; it does not compare ZFS
+dataset properties, snapshots, quotas, reservations, or encryption settings.
+
 ## SSH Setup
 
 Create a dedicated key on the source server if one does not already exist: