presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/FileStorageService.java/FileStorageService/getStorageShards
class FileStorageService:    @Override
    public Set<UUID> getStorageShards()
    {
        ImmutableSet.Builder<UUID> shards = ImmutableSet.builder();
        for (File level1 : listFiles(baseStorageDir, FileStorageService::isHexDirectory)) {
            for (File level2 : listFiles(level1, FileStorageService::isHexDirectory)) {
                for (File file : listFiles(level2, path -> true)) {
                    if (file.isFile()) {
                        uuidFromFileName(file.getName()).ifPresent(shards::add);
                    }
                }
            }
        }
        return shards.build();
    }