我有一个磁盘，有两个分区：
# fdisk -l
Disk /dev/mmcblk0: 7381 MB, 7381975040 bytes
4 heads, 16 sectors/track, 225280 cylinders
Units = cylinders of 64 * 512 = 32768 bytes
Device Boot Start End Blocks Id System
/dev/mmcblk0p1 * 33 32800 1048576 83 Linux
/dev/mmcblk0p2 32801 65568 1048576 83 Linux
其中/dev/mmcblk0p2保存覆盖文件系统。
我卸载并复制 ext4 USB 记忆棒上文件中的第二个分区 ( /media/usb/sda1)：
# umount /overlay/
# dd if=/dev/mmcblk0p2 of=/media/usb/sda1/overlay.img
该文件显示：
# file overlay.img
overlay.img: Linux rev 1.0 ext4 filesystem data, UUID=79213fb6-180c-474c-ba7b-2567a62a869a (needs journal recovery) (extents) (large files) (huge files)
如果我尝试安装它，它会失败：
# mount -t ext4 -o loop overlay.img mnt
[ 931.883626] EXT4-fs error (device loop0): ext4_map_blocks:591: inode #8: block 131098: comm mount: lblock 26 mapped to illegal pblock 131098 (length 1)
[ 931.921489] jbd2_journal_bmap: journal block not found at offset 26 on loop0-8
[ 931.928718] JBD2: bad block at offset 26
[ 931.932626] JBD2: IO error -5 recovering block 26 in log
[ 931.937968] EXT4-fs error (device loop0): ext4_map_blocks:591: inode #8: block 131099: comm mount: lblock 27 mapped to illegal pblock 131099 (length 1)
[ 931.998314] jbd2_journal_bmap: journal block not found at offset 27 on loop0-8
[ 932.005560] JBD2: bad block at offset 27
[ 932.009484] JBD2: IO error -5 recovering block 27 in log
[ 932.014810] EXT4-fs error (device loop0): ext4_map_blocks:591: inode #8: block 131100: comm mount: lblock 28 mapped to illegal pblock 131100 (length 1)
[ 932.041620] jbd2_journal_bmap: journal block not found at offset 28 on loop0-8
[ 932.048834] JBD2: bad block at offset 28
[ 932.052745] JBD2: IO error -5 recovering block 28 in log
[ 932.058051] EXT4-fs error (device loop0): ext4_map_blocks:591: inode #8: block 131101: comm mount: lblock 29 mapped to illegal pblock 131101 (length 1)
[ 932.082502] jbd2_journal_bmap: journal block not found at offset 29 on loop0-8
[ 932.089716] JBD2: bad block at offset 29
[ 932.093629] JBD2: IO error -5 recovering block 29 in log
[ 932.098937] EXT4-fs error (device loop0): ext4_map_blocks:591: inode #8: block 131102: comm mount: lblock 30 mapped to illegal pblock 131102 (length 1)
[ 932.127150] jbd2_journal_bmap: journal block not found at offset 30 on loop0-8
[ 932.134369] JBD2: bad block at offset 30
[ 933.372932] JBD2: recovery failed
[ 933.376238] EXT4-fs (loop0): error loading journal
mount: mounting /dev/loop0 on mnt failed: Input/output error
并mount更改文件：
# file overlay.img
overlay.img: data
我的设备是ARM，上面有busybox v1.24.1。
那么，如何复制整个分区呢？如何挂载它，它是否修改了我的文件？我需要额外做一些事情才能正确安装它吗？