Add zvol existence check and creation for iSCSI extents

client.py:
- check_iscsi_zvols(): queries pool.dataset.query for VOLUME type,
  returns list of missing zvol names
- create_zvol(): creates a single zvol via pool.dataset.create
- create_missing_zvols(): opens a fresh connection and creates a
  batch of zvols from a {name: volsize_bytes} dict

summary.py:
- Add zvols_to_check and missing_zvols list fields
- Report shows a WARNING block listing missing zvols when present

migrate.py:
- _migrate_iscsi_extents() populates summary.zvols_to_check with
  the dataset name for each DISK-type extent during dry run

cli.py:
- Add _parse_size() to parse human-friendly size strings
  (100G, 500GiB, 1T, etc.) to bytes
- run() calls check_iscsi_zvols() during dry run and stores results
  in summary.missing_zvols
- Wizard prompts for size and creates missing zvols after the dry
  run report, before asking the user to confirm the live run

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

truenas_migrate/cli.py

@@ -54,7 +54,7 @@ from pathlib import Path
 from typing import Optional
 
 from .archive import parse_archive, list_archive_and_exit
-from .client import TrueNASClient, check_dataset_paths, create_missing_datasets
+from .client import TrueNASClient, check_dataset_paths, create_missing_datasets, check_iscsi_zvols, create_missing_zvols
 from .colors import log, _bold, _bold_cyan, _bold_red, _bold_yellow, _cyan, _dim, _green, _yellow
 from .csv_source import parse_csv_sources
 from .migrate import migrate_smb_shares, migrate_nfs_shares, migrate_iscsi
@@ -112,6 +112,11 @@ async def run(
                 client, summary.paths_to_create,
             )
 
+        if args.dry_run and summary.zvols_to_check:
+            summary.missing_zvols = await check_iscsi_zvols(
+                client, summary.zvols_to_check,
+            )
+
     return summary
 
 
@@ -119,6 +124,24 @@ async def run(
 # Interactive wizard helpers
 # ─────────────────────────────────────────────────────────────────────────────
 
+def _parse_size(s: str) -> int:
+    """Parse a human-friendly size string to bytes.  E.g. '100G', '500GiB', '1T'."""
+    s = s.strip().upper()
+    for suffix, mult in [
+        ("PIB", 1 << 50), ("PB", 1 << 50), ("P", 1 << 50),
+        ("TIB", 1 << 40), ("TB", 1 << 40), ("T", 1 << 40),
+        ("GIB", 1 << 30), ("GB", 1 << 30), ("G", 1 << 30),
+        ("MIB", 1 << 20), ("MB", 1 << 20), ("M", 1 << 20),
+        ("KIB", 1 << 10), ("KB", 1 << 10), ("K", 1 << 10),
+    ]:
+        if s.endswith(suffix):
+            try:
+                return int(float(s[:-len(suffix)]) * mult)
+            except ValueError:
+                pass
+    return int(s)  # plain bytes
+
+
 def _find_debug_archives(directory: str = ".") -> list[Path]:
     """Return sorted list of TrueNAS debug archives found in *directory*."""
     patterns = ("*.tgz", "*.tar.gz", "*.tar", "*.txz", "*.tar.xz")
@@ -405,6 +428,29 @@ def interactive_mode() -> None:
                 ))
                 print()
 
+    if dry_summary.missing_zvols:
+        print(f"\n  {len(dry_summary.missing_zvols)} zvol(s) need to be created for iSCSI extents:")
+        for z in dry_summary.missing_zvols:
+            print(f"    • {z}")
+        print()
+        if _confirm(f"Create these {len(dry_summary.missing_zvols)} zvol(s) on {host} now?"):
+            zvol_sizes: dict[str, int] = {}
+            for zvol in dry_summary.missing_zvols:
+                while True:
+                    raw = _prompt(f"  Size for {zvol} (e.g. 100G, 500GiB, 1T)").strip()
+                    if not raw:
+                        print("  Size is required.")
+                        continue
+                    try:
+                        zvol_sizes[zvol] = _parse_size(raw)
+                        break
+                    except ValueError:
+                        print(f"  Cannot parse {raw!r} — try a format like 100G or 500GiB.")
+            asyncio.run(create_missing_zvols(
+                host=host, port=port, api_key=api_key, zvols=zvol_sizes,
+            ))
+            print()
+
     if not _confirm(f"Apply these changes to {host}?"):
         print("Aborted – no changes made.")
         sys.exit(0)