ECS云服务器分区时出现Unabletoopendev/xvdb

我是新手，刚刚申请了个免费使用的，操作好这边就不行了
求高手指点
Welcome to aliyun Elastic Compute Service!

[root@iZ948mpkyhgZ ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda1              20G  1.1G   19G   6% /
tmpfs                 501M     0  501M   0% /dev/shm
[root@iZ948mpkyhgZ ~]# fdisk -1
fdisk: invalid option -- 1

Usage: fdisk [-b SSZ] [-u] DISK     Change partition table
       fdisk -l [-b SSZ] [-u] DISK  List partition table(s)
       fdisk -s PARTITION           Give partition size(s) in blocks
       fdisk -v                     Give fdisk version
Here DISK is something like /dev/hdb or /dev/sda
and PARTITION is something like /dev/hda7
-u: give Start and End in sector (instead of cylinder) units
-b 2048: (for certain MO disks) use 2048-byte sectors
[root@iZ948mpkyhgZ ~]# fdisk -S 56 /dev/xvdb

Unable to open /dev/xvdb