分区的过程正常：

[root@db1 /]# fdisk -l
Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14         650     5116702+  83  Linux
/dev/sda3             651         841     1534207+  82  Linux swap / Solaris
[root@db1 /]# fdisk /dev/sda
The number of cylinders for this disk is set to 2610.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Selected partition 4
First cylinder (842-2610, default 842):
Using default value 842
Last cylinder or +size or +sizeM or +sizeK (842-2610, default 2610):
Using default value 2610
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

再次查看，分区已经划好：

[root@db1 /]# fdisk -l
Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14         650     5116702+  83  Linux
/dev/sda3             651         841     1534207+  82  Linux swap / Solaris
/dev/sda4             842        2610    14209492+  83  Linux

 但是格式化的时候，报错：

[root@db1 /]# mkfs -t ext3 /dev/sda4
mke2fs 1.39 (29-May-2016)
Could not stat /dev/sda4 --- No such file or directory
The device apparently does not exist; did you specify it correctly?

  解决方法：执行下partprobe 命令

        partprobe包含在parted的rpm软件包中。partprobe可以修改kernel中分区表，使kernel重新读取分区表。 因此，使用该命令就可以创建分区并且在不重新启动机器的情况下系统能够识别这些分区。

 查看是否安装该命令：

[root@db1 dev]# rpm -q parted
parted-1.8.1-23.el5

 我们执行一下该命令：

[root@db1 dev]# partprobe
Warning: Unable to open /dev/hdc read-write (Read-only file system).  /dev/hdc has been opened read-only.

 然后在格式化，就ok了：

[root@db1 dev]# mkfs -t ext3 /dev/sda4
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
1778880 inodes, 3552373 blocks
177618 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=3640655872
109 block groups
32768 blocks per group, 32768 fragments per group
16320 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208
Writing inode tables: done    
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 38 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.