diff --git a/core/BackgroundJobs/PreviewMigrationJob.php b/core/BackgroundJobs/PreviewMigrationJob.php
index 5ca3de9286a35..e5bd2b4a49450 100644
--- a/core/BackgroundJobs/PreviewMigrationJob.php
+++ b/core/BackgroundJobs/PreviewMigrationJob.php
@@ -12,11 +12,10 @@
 use OC\Preview\PreviewMigrationService;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\BackgroundJob\TimedJob;
-use OCP\DB\IResult;
+use OCP\Files\FileInfo;
 use OCP\Files\IRootFolder;
 use OCP\IAppConfig;
 use OCP\IConfig;
-use OCP\IDBConnection;
 use Override;
 use Psr\Log\LoggerInterface;
 
@@ -27,7 +26,6 @@ public function __construct(
 		ITimeFactory $time,
 		private readonly IAppConfig $appConfig,
 		private readonly IConfig $config,
-		private readonly IDBConnection $connection,
 		private readonly IRootFolder $rootFolder,
 		private readonly PreviewMigrationService $migrationService,
 		private readonly LoggerInterface $logger,
@@ -45,79 +43,62 @@ protected function run(mixed $argument): void {
 			return;
 		}
 
-		$startTime = time();
-		while (true) {
-			$qb = $this->connection->getQueryBuilder();
-			$qb->select('path')
-				->from('filecache')
-				->where($qb->expr()->orX(
-					// Hierarchical preview folder structure
-					$qb->expr()->like('path', $qb->createNamedParameter($this->previewRootPath . '%/%/%/%/%/%/%/%/%')),
-					// Legacy flat preview folder structure
-					$qb->expr()->like('path', $qb->createNamedParameter($this->previewRootPath . '%/%.%'))
-				))->andWhere(
-					$qb->expr()->eq('storage', $qb->createNamedParameter($this->rootFolder->getMountPoint()->getNumericStorageId()))
-				)
-				->hintShardKey('storage', $this->rootFolder->getMountPoint()->getNumericStorageId())
-				->setMaxResults(100);
-
-			$result = $qb->executeQuery();
-			$foundPreviews = $this->processQueryResult($result);
-
-			if (!$foundPreviews) {
-				break;
-			}
+		$storage = $this->rootFolder->getMountPoint()->getStorage();
+		if ($storage === null) {
+			$this->appConfig->setValueBool('core', 'previewMovedDone', true);
+			return;
+		}
 
-			// Stop if execution time is more than one hour.
-			if (time() - $startTime > 3600) {
-				return;
-			}
+		$cache = $storage->getCache();
+		$previewRootId = $cache->getId(rtrim($this->previewRootPath, '/'));
+		if ($previewRootId === -1) {
+			// No previews have ever been generated on this instance.
+			$this->appConfig->setValueBool('core', 'previewMovedDone', true);
+			return;
 		}
 
-		$this->appConfig->setValueBool('core', 'previewMovedDone', true);
-	}
+		$startTime = time();
 
-	private function processQueryResult(IResult $result): bool {
-		$foundPreview = false;
-		$fileIds = [];
-		$flatFileIds = [];
-		while ($row = $result->fetch()) {
-			$pathSplit = explode('/', $row['path']);
-			assert(count($pathSplit) >= 2);
-			$fileId = (int)$pathSplit[count($pathSplit) - 2];
-			if (count($pathSplit) === 11) {
-				// Hierarchical structure
-				if (!in_array($fileId, $fileIds)) {
-					$fileIds[] = $fileId;
-				}
-			} else {
-				// Flat structure
-				if (!in_array($fileId, $flatFileIds)) {
-					$flatFileIds[] = $fileId;
+		// Walk the preview folder tree via the `parent` column, which is indexed on
+		// every supported database platform.
+		//
+		// Depth from the preview root tells us which structure a leaf folder holds:
+		// - depth 1: legacy flat structure, e.g. preview/<fileid>/<size>.png
+		// - depth 8: hierarchical structure, e.g. preview/a/b/c/d/e/f/g/<fileid>/<size>.png
+		$foldersToVisit = [[$previewRootId, '', 0]];
+
+		while ($foldersToVisit !== []) {
+			[$folderId, $folderName, $depth] = array_pop($foldersToVisit);
+
+			// Collect the actual preview files here so migrateFileId() doesn't need to
+			// list this folder's contents a second time.
+			$previewEntries = [];
+			foreach ($cache->getFolderContentsById($folderId) as $entry) {
+				if ($entry->getMimeType() === FileInfo::MIMETYPE_FOLDER) {
+					$foldersToVisit[] = [$entry->getId(), $entry->getName(), $depth + 1];
+				} else {
+					$previewEntries[] = $entry;
 				}
 			}
-			$foundPreview = true;
-		}
 
-		foreach ($fileIds as $fileId) {
-			try {
-				$this->migrationService->migrateFileId($fileId, flatPath: false);
-			} catch (\Exception $e) {
-				$this->logger->error('Failed to migrate preview with fileId: ' . $fileId . ' (hierarchical file structure)', [
-					'exception' => $e,
-				]);
+			if ($previewEntries === [] || !ctype_digit($folderName)) {
+				continue;
 			}
-		}
 
-		foreach ($flatFileIds as $fileId) {
 			try {
-				$this->migrationService->migrateFileId($fileId, flatPath: true);
+				$this->migrationService->migrateFileId((int)$folderName, flatPath: $depth === 1, entries: $previewEntries);
 			} catch (\Exception $e) {
-				$this->logger->error('Failed to migrate preview with fileId: ' . $fileId . ' (legacy file structure)', [
+				$this->logger->error('Failed to migrate preview with fileId: ' . $folderName, [
 					'exception' => $e,
 				]);
 			}
+
+			// Stop if execution time is more than one hour.
+			if (time() - $startTime > 3600) {
+				return;
+			}
 		}
-		return $foundPreview;
+
+		$this->appConfig->setValueBool('core', 'previewMovedDone', true);
 	}
 }
diff --git a/lib/private/Preview/PreviewMigrationService.php b/lib/private/Preview/PreviewMigrationService.php
index 555bd3884474b..377950da84952 100644
--- a/lib/private/Preview/PreviewMigrationService.php
+++ b/lib/private/Preview/PreviewMigrationService.php
@@ -14,7 +14,9 @@
 use OC\Preview\Db\PreviewMapper;
 use OC\Preview\Storage\StorageFactory;
 use OCP\DB\Exception;
+use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\Files\AppData\IAppDataFactory;
+use OCP\Files\Cache\ICacheEntry;
 use OCP\Files\IAppData;
 use OCP\Files\IMimeTypeDetector;
 use OCP\Files\IMimeTypeLoader;
@@ -44,44 +46,43 @@ public function __construct(
 	}
 
 	/**
-	 * @param array<string|int, string[]> $previewFolders
+	 * @param list<ICacheEntry|SimpleFile>|null $entries Preview file entries already fetched by the caller.
 	 * @return Preview[]
 	 */
-	public function migrateFileId(int $fileId, bool $flatPath): array {
+	public function migrateFileId(int $fileId, bool $flatPath, ?array $entries = null): array {
 		$previews = [];
 		$internalPath = $this->getInternalFolder((string)$fileId, $flatPath);
-		try {
-			$folder = $this->appData->getFolder($internalPath);
-		} catch (NotFoundException) {
-			return [];
+
+		if ($entries === null) {
+			try {
+				$entries = $this->appData->getFolder($internalPath)->getDirectoryListing();
+			} catch (NotFoundException) {
+				return [];
+			}
 		}
 
 		/**
-		 * @var list<array{file: SimpleFile, preview: Preview}> $previewFiles
+		 * @var list<Preview> $previewsToInsert
 		 */
-		$previewFiles = [];
+		$previewsToInsert = [];
 
-		foreach ($folder->getDirectoryListing() as $previewFile) {
-			$path = $fileId . '/' . $previewFile->getName();
-			/** @var SimpleFile $previewFile */
+		foreach ($entries as $entry) {
+			$path = $fileId . '/' . $entry->getName();
 			$preview = Preview::fromPath($path, $this->mimeTypeDetector);
 			if ($preview === false) {
 				$this->logger->error('Unable to import old preview at path.');
 				continue;
 			}
 			$preview->generateId();
-			$preview->setSize($previewFile->getSize());
-			$preview->setMtime($previewFile->getMtime());
-			$preview->setOldFileId($previewFile->getId());
+			$preview->setSize($entry->getSize());
+			$preview->setMtime($entry->getMTime());
+			$preview->setOldFileId($entry->getId());
 			$preview->setEncrypted(false);
 
-			$previewFiles[] = [
-				'file' => $previewFile,
-				'preview' => $preview,
-			];
+			$previewsToInsert[] = $preview;
 		}
 
-		if (empty($previewFiles)) {
+		if (empty($previewsToInsert)) {
 			$this->deleteFolder($internalPath);
 
 			return $previews;
@@ -98,56 +99,51 @@ public function migrateFileId(int $fileId, bool $flatPath): array {
 		$cursor->closeCursor();
 
 		if ($result !== false) {
-			foreach ($previewFiles as $previewFile) {
-				/** @var Preview $preview */
-				$preview = $previewFile['preview'];
-				/** @var SimpleFile $file */
-				$file = $previewFile['file'];
-				$preview->setStorageId($result['storage']);
-				$preview->setEtag($result['etag']);
-				$preview->setSourceMimeType($this->mimeTypeLoader->getMimetypeById((int)$result['mimetype']));
-				$preview->generateId();
-				try {
-					$preview = $this->previewMapper->insert($preview);
-				} catch (Exception $e) {
-					if ($e->getReason() !== Exception::REASON_UNIQUE_CONSTRAINT_VIOLATION) {
-						throw $e;
+			$oldFileIdsToDelete = [];
+			try {
+				foreach ($previewsToInsert as $preview) {
+					$preview->setStorageId($result['storage']);
+					$preview->setEtag($result['etag']);
+					$preview->setSourceMimeType($this->mimeTypeLoader->getMimetypeById((int)$result['mimetype']));
+					$preview->generateId();
+					try {
+						$preview = $this->previewMapper->insert($preview);
+					} catch (Exception $e) {
+						if ($e->getReason() !== Exception::REASON_UNIQUE_CONSTRAINT_VIOLATION) {
+							throw $e;
+						}
+
+						// We already have this preview in the preview table, skip
+						$oldFileIdsToDelete[] = $preview->getOldFileId();
+						continue;
 					}
 
-					$delete = $this->connection->getQueryBuilder();
-					// We already have this preview in the preview table, skip
-					$delete->delete('filecache')
-						->where($delete->expr()->eq('fileid', $delete->createNamedParameter($file->getId())))
-						->hintShardKey('storage', $this->rootFolder->getMountPoint()->getNumericStorageId())
-						->executeStatement();
-					continue;
-				}
+					try {
+						$this->storageFactory->migratePreview($preview);
+						// Do not delete the old file via a Node here, as that would also
+						// delete it from the file system; only its filecache row is stale.
+					} catch (\Exception $e) {
+						$this->previewMapper->delete($preview);
+						throw $e;
+					}
 
-				try {
-					$this->storageFactory->migratePreview($preview, $file);
-					$qb = $this->connection->getQueryBuilder();
-					$qb->delete('filecache')
-						->where($qb->expr()->eq('fileid', $qb->createNamedParameter($file->getId())))
-						->hintShardKey('storage', $this->rootFolder->getMountPoint()->getNumericStorageId())
-						->executeStatement();
-					// Do not call $file->delete() as this will also delete the file from the file system
-				} catch (\Exception $e) {
-					$this->previewMapper->delete($preview);
-					throw $e;
+					$oldFileIdsToDelete[] = $preview->getOldFileId();
+					$previews[] = $preview;
 				}
-
-				$previews[] = $preview;
+			} finally {
+				$this->deleteOldFileCacheEntries($oldFileIdsToDelete);
 			}
 		} else {
-			// No matching fileId, delete preview
+			// No matching fileId, delete the orphaned preview files themselves.
 			try {
+				$folder = $this->appData->getFolder($internalPath);
 				$this->connection->beginTransaction();
-				foreach ($previewFiles as $previewFile) {
-					/** @var SimpleFile $file */
-					$file = $previewFile['file'];
+				foreach ($folder->getDirectoryListing() as $file) {
 					$file->delete();
 				}
 				$this->connection->commit();
+			} catch (NotFoundException) {
+				// Folder already gone, nothing to clean up.
 			} catch (Exception) {
 				$this->connection->rollback();
 			}
@@ -165,6 +161,23 @@ private static function getInternalFolder(string $name, bool $flatPath): string
 		return implode('/', str_split(substr(md5($name), 0, 7))) . '/' . $name;
 	}
 
+	/**
+	 * @param list<int> $fileIds
+	 */
+	private function deleteOldFileCacheEntries(array $fileIds): void {
+		if ($fileIds === []) {
+			return;
+		}
+
+		foreach (array_chunk($fileIds, 1000) as $chunk) {
+			$qb = $this->connection->getQueryBuilder();
+			$qb->delete('filecache')
+				->where($qb->expr()->in('fileid', $qb->createNamedParameter($chunk, IQueryBuilder::PARAM_INT_ARRAY)))
+				->hintShardKey('storage', $this->rootFolder->getMountPoint()->getNumericStorageId())
+				->executeStatement();
+		}
+	}
+
 	private function deleteFolder(string $path): void {
 		$current = $path;
 
@@ -185,14 +198,38 @@ private function deleteFolder(string $path): void {
 				break;
 			}
 
-			try {
-				$folder = $this->appData->getFolder($current);
-			} catch (NotFoundException) {
-				break;
-			}
-			if (count($folder->getDirectoryListing()) !== 0) {
+			if ($this->folderHasChildren($rootFolderId, $this->previewRootPath . $current)) {
 				break;
 			}
 		}
 	}
+
+	private function folderHasChildren(int $storageId, string $path): bool {
+		$qb = $this->connection->getQueryBuilder();
+		$qb->select('fileid')
+			->from('filecache')
+			->where($qb->expr()->eq('path_hash', $qb->createNamedParameter(md5($path))))
+			->andWhere($qb->expr()->eq('storage', $qb->createNamedParameter($storageId)))
+			->setMaxResults(1);
+		$cursor = $qb->executeQuery();
+		$folderId = $cursor->fetchOne();
+		$cursor->closeCursor();
+
+		if ($folderId === false) {
+			// The folder itself is already gone, nothing to check.
+			return false;
+		}
+
+		$qb = $this->connection->getQueryBuilder();
+		$qb->select('fileid')
+			->from('filecache')
+			->where($qb->expr()->eq('parent', $qb->createNamedParameter((int)$folderId)))
+			->andWhere($qb->expr()->eq('storage', $qb->createNamedParameter($storageId)))
+			->setMaxResults(1);
+		$cursor = $qb->executeQuery();
+		$hasChild = $cursor->fetchOne() !== false;
+		$cursor->closeCursor();
+
+		return $hasChild;
+	}
 }
diff --git a/lib/private/Preview/Storage/IPreviewStorage.php b/lib/private/Preview/Storage/IPreviewStorage.php
index f7b60b9cc9be3..28d2dc53ef577 100644
--- a/lib/private/Preview/Storage/IPreviewStorage.php
+++ b/lib/private/Preview/Storage/IPreviewStorage.php
@@ -10,7 +10,6 @@
 namespace OC\Preview\Storage;
 
 use Exception;
-use OC\Files\SimpleFS\SimpleFile;
 use OC\Preview\Db\Preview;
 use OCP\Files\NotFoundException;
 use OCP\Files\NotPermittedException;
@@ -42,7 +41,7 @@ public function deletePreview(Preview $preview): void;
 	 * To remove at some point
 	 * @throws Exception
 	 */
-	public function migratePreview(Preview $preview, SimpleFile $file): void;
+	public function migratePreview(Preview $preview): void;
 
 	/**
 	 * @throws NotPermittedException
diff --git a/lib/private/Preview/Storage/LocalPreviewStorage.php b/lib/private/Preview/Storage/LocalPreviewStorage.php
index 99427b74b2901..4d9d594089e40 100644
--- a/lib/private/Preview/Storage/LocalPreviewStorage.php
+++ b/lib/private/Preview/Storage/LocalPreviewStorage.php
@@ -12,7 +12,6 @@
 
 use LogicException;
 use OC;
-use OC\Files\SimpleFS\SimpleFile;
 use OC\Preview\Db\Preview;
 use OC\Preview\Db\PreviewMapper;
 use OCP\DB\Exception;
@@ -93,7 +92,7 @@ private function createParentFiles(string $path): void {
 	}
 
 	#[Override]
-	public function migratePreview(Preview $preview, SimpleFile $file): void {
+	public function migratePreview(Preview $preview): void {
 		// legacy flat directory
 		$sourcePath = $this->getPreviewRootFolder() . $preview->getFileId() . '/' . $preview->getName();
 		if (!file_exists($sourcePath)) {
diff --git a/lib/private/Preview/Storage/ObjectStorePreviewStorage.php b/lib/private/Preview/Storage/ObjectStorePreviewStorage.php
index 713d39f9b0b38..f77da26eaea95 100644
--- a/lib/private/Preview/Storage/ObjectStorePreviewStorage.php
+++ b/lib/private/Preview/Storage/ObjectStorePreviewStorage.php
@@ -12,7 +12,6 @@
 
 use Icewind\Streams\CountWrapper;
 use OC\Files\ObjectStore\PrimaryObjectStoreConfig;
-use OC\Files\SimpleFS\SimpleFile;
 use OC\Preview\Db\Preview;
 use OC\Preview\Db\PreviewMapper;
 use OCP\Files\NotPermittedException;
@@ -95,7 +94,7 @@ public function deletePreview(Preview $preview): void {
 	}
 
 	#[Override]
-	public function migratePreview(Preview $preview, SimpleFile $file): void {
+	public function migratePreview(Preview $preview): void {
 		// Just set the Preview::bucket and Preview::objectStore
 		$this->getObjectStoreInfoForNewPreview($preview, migration: true);
 		$this->previewMapper->update($preview);
diff --git a/lib/private/Preview/Storage/StorageFactory.php b/lib/private/Preview/Storage/StorageFactory.php
index 69c7776c42e51..39cd11e09cfbd 100644
--- a/lib/private/Preview/Storage/StorageFactory.php
+++ b/lib/private/Preview/Storage/StorageFactory.php
@@ -10,7 +10,6 @@
 namespace OC\Preview\Storage;
 
 use OC\Files\ObjectStore\PrimaryObjectStoreConfig;
-use OC\Files\SimpleFS\SimpleFile;
 use OC\Preview\Db\Preview;
 use OCP\Server;
 use Override;
@@ -53,8 +52,8 @@ private function getBackend(): IPreviewStorage {
 	}
 
 	#[Override]
-	public function migratePreview(Preview $preview, SimpleFile $file): void {
-		$this->getBackend()->migratePreview($preview, $file);
+	public function migratePreview(Preview $preview): void {
+		$this->getBackend()->migratePreview($preview);
 	}
 
 	#[Override]
diff --git a/tests/lib/Preview/PreviewMigrationJobTest.php b/tests/lib/Preview/PreviewMigrationJobTest.php
index fe9cd96879959..dcd57464f0d1e 100644
--- a/tests/lib/Preview/PreviewMigrationJobTest.php
+++ b/tests/lib/Preview/PreviewMigrationJobTest.php
@@ -10,6 +10,7 @@
 namespace lib\Preview;
 
 use OC\Core\BackgroundJobs\PreviewMigrationJob;
+use OC\Preview\Db\Preview;
 use OC\Preview\Db\PreviewMapper;
 use OC\Preview\PreviewMigrationService;
 use OC\Preview\PreviewService;
@@ -115,11 +116,21 @@ public function testMigrationLegacyPath(): void {
 		$this->assertEquals(2, count($folder->getDirectoryListing()));
 		$this->assertEquals(0, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
 
-		$job = new PreviewMigrationJob(
+		$job = $this->createJob();
+		$this->invokePrivate($job, 'run', [[]]);
+		$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
+		$this->assertEquals(2, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
+	}
+
+	private static function getInternalFolder(string $name): string {
+		return implode('/', str_split(substr(md5($name), 0, 7))) . '/' . $name;
+	}
+
+	private function createJob(): PreviewMigrationJob {
+		return new PreviewMigrationJob(
 			Server::get(ITimeFactory::class),
 			$this->appConfig,
 			$this->config,
-			Server::get(IDBConnection::class),
 			Server::get(IRootFolder::class),
 			new PreviewMigrationService(
 				$this->config,
@@ -134,13 +145,107 @@ public function testMigrationLegacyPath(): void {
 			),
 			$this->logger,
 		);
-		$this->invokePrivate($job, 'run', [[]]);
+	}
+
+	private function insertFilecacheRow(string $path, string $etag): int {
+		$qb = $this->db->getQueryBuilder();
+		$qb->insert('filecache')
+			->values([
+				'storage' => $qb->createNamedParameter(1),
+				'path' => $qb->createNamedParameter($path),
+				'path_hash' => $qb->createNamedParameter(md5($path)),
+				'parent' => $qb->createNamedParameter(0),
+				'name' => $qb->createNamedParameter(basename($path)),
+				'mimetype' => $qb->createNamedParameter(42),
+				'size' => $qb->createNamedParameter(1000),
+				'mtime' => $qb->createNamedParameter(1000),
+				'storage_mtime' => $qb->createNamedParameter(1000),
+				'encrypted' => $qb->createNamedParameter(0),
+				'unencrypted_size' => $qb->createNamedParameter(0),
+				'etag' => $qb->createNamedParameter($etag),
+				'permissions' => $qb->createNamedParameter(0),
+				'checksum' => $qb->createNamedParameter($etag),
+			])->executeStatement();
+		return $qb->getLastInsertId();
+	}
+
+	private function deleteFilecacheRow(int $fileId): void {
+		$qb = $this->db->getQueryBuilder();
+		$qb->delete('filecache')
+			->where($qb->expr()->eq('fileid', $qb->createNamedParameter($fileId)))
+			->executeStatement();
+	}
+
+	#[TestDox('A single run must migrate multiple different fileids in one pass, mixing both folder structures')]
+	public function testMigrationMultipleFileIds(): void {
+		$otherFileId = $this->insertFilecacheRow('test/def', 'xyz123');
+
+		try {
+			$flatFolder = $this->previewAppData->newFolder('5');
+			$flatFolder->newFile('64-64-crop.jpg', 'abcdefg');
+
+			$hierFolder = $this->previewAppData->newFolder(self::getInternalFolder((string)$otherFileId));
+			$hierFolder->newFile('128-128.png', 'abcdefg');
+
+			$this->invokePrivate($this->createJob(), 'run', [[]]);
+
+			$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
+			$this->assertEquals(1, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
+			$this->assertEquals(1, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile($otherFileId))));
+		} finally {
+			$this->deleteFilecacheRow($otherFileId);
+		}
+	}
+
+	#[TestDox('Re-migrating a preview that already exists must skip the insert and still clean up the stale filecache row')]
+	public function testMigrationSkipsDuplicatePreview(): void {
+		$folder = $this->previewAppData->newFolder('5');
+		$folder->newFile('64-64-crop.jpg', 'abcdefg');
+
+		// Simulate a preview that was already migrated by an earlier, interrupted run:
+		// same fileid/width/height/mimetype/cropped/version as what this migration
+		// would produce for the file created above, so the insert below hits the
+		// `previews_file_uniq_idx` unique constraint.
+		$existing = Preview::fromPath('5/64-64-crop.jpg', $this->mimeTypeDetector);
+		$this->assertNotFalse($existing);
+		$existing->setFileId(5);
+		$existing->setStorageId(1);
+		$existing->setSourceMimeType('image/png');
+		$existing->setEtag('abcdefg');
+		$existing->setSize(7);
+		$existing->setMtime(1000);
+		$existing->setEncrypted(false);
+		$existing->generateId();
+		$this->previewMapper->insert($existing);
+
+		$this->invokePrivate($this->createJob(), 'run', [[]]);
+
+		// No duplicate preview row was inserted, but the legacy folder and its stale
+		// filecache row were still cleaned up.
 		$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
-		$this->assertEquals(2, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
+		$this->assertEquals(1, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
 	}
 
-	private static function getInternalFolder(string $name): string {
-		return implode('/', str_split(substr(md5($name), 0, 7))) . '/' . $name;
+	#[TestDox('An orphaned preview folder whose source file no longer exists must be deleted, not migrated')]
+	public function testMigrationDeletesOrphanedPreview(): void {
+		$orphanFileId = 9999998;
+		$folder = $this->previewAppData->newFolder((string)$orphanFileId);
+		$folder->newFile('64-64-crop.jpg', 'abcdefg');
+
+		$this->invokePrivate($this->createJob(), 'run', [[]]);
+
+		$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
+		$this->assertEquals(0, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile($orphanFileId))));
+	}
+
+	#[TestDox('run() must complete without error when there is nothing to migrate')]
+	public function testMigrationWithoutAnyPreviews(): void {
+		$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
+
+		$this->invokePrivate($this->createJob(), 'run', [[]]);
+
+		$this->assertEquals(0, count($this->previewAppData->getDirectoryListing()));
+		$this->assertEquals(0, count(iterator_to_array($this->previewMapper->getAvailablePreviewsForFile(5))));
 	}
 
 	#[TestDox("Test the migration from the 'new' nested hierarchy to the database format")]
@@ -157,7 +262,6 @@ public function testMigrationPath(): void {
 			Server::get(ITimeFactory::class),
 			$this->appConfig,
 			$this->config,
-			Server::get(IDBConnection::class),
 			Server::get(IRootFolder::class),
 			new PreviewMigrationService(
 				$this->config,
@@ -203,7 +307,6 @@ public function testMigrationPathWithVersion(): void {
 			Server::get(ITimeFactory::class),
 			$this->appConfig,
 			$this->config,
-			Server::get(IDBConnection::class),
 			Server::get(IRootFolder::class),
 			new PreviewMigrationService(
 				$this->config,