在安装FreeBSD的时候，每次安装错误，再次安装的时候，就说找不到zfs盘，手工去找到盘，想删除zfs分区，也说不能删除

umount /mnt 报错

后来是把/mnt下面的目录一个一个删除，最后删除/mnt，问题解决。

zfs unmount /mnt
cannot unmount '/mnt': pool or dataset is busyumount /mnt/home
# umount /mnt/*
umount: /mnt/boot: not a file system root directory
umount: /mnt/dev: not a file system root directory
umount: /mnt/home: not a file system root directory
umount: /mnt/usr: not a file system root directory
umount: /mnt/var: not a file system root directory
# df
Filesystem                       1K-blocks   Used    Avail Capacity  Mounted on
/dev/iso9660/14_1_BETA3_AMD64_BO    445288 445288        0   100%    /
devfs                                    1      0        1     0%    /dev
tmpfs                                20480    228    20252     1%    /tmp
tmpfs                                32768    120    32648     0%    /var
zroot/ROOT/default                17774696    120 17774576     0%    /mnt
zroot/usr/ports                   17774672     96 17774576     0%    /mnt/usr/ports
zroot/usr/src                     17774672     96 17774576     0%    /mnt/usr/src
zroot/var/audit                   17774672     96 17774576     0%    /mnt/var/audit
zroot/var/crash                   17774672     96 17774576     0%    /mnt/var/crash
zroot/var/log                     17774672     96 17774576     0%    /mnt/var/log
zroot/var/mail                    17774672     96 17774576     0%    /mnt/var/mail
zroot/var/tmp                     17774672     96 17774576     0%    /mnt/var/tmp
# umount /mnt/usr/*
umount: /mnt/usr/freebsd-dist: not a file system root directory
# umount /mnt/var/*
# umount /mnt/var/*
umount: /mnt/var/audit: not a file system root directory
umount: /mnt/var/crash: not a file system root directory
umount: /mnt/var/log: not a file system root directory
umount: /mnt/var/mail: not a file system root directory
umount: /mnt/var/tmp: not a file system root directory
# df
Filesystem                       1K-blocks   Used    Avail Capacity  Mounted on
/dev/iso9660/14_1_BETA3_AMD64_BO    445288 445288        0   100%    /
devfs                                    1      0        1     0%    /dev
tmpfs                                20480    228    20252     1%    /tmp
tmpfs                                32768    120    32648     0%    /var
zroot/ROOT/default                17774696    120 17774576     0%    /mnt
# umount /mnt
# df
Filesystem                       1K-blocks   Used Avail Capacity  Mounted on
/dev/iso9660/14_1_BETA3_AMD64_BO    445288 445288     0   100%    /
devfs                                    1      0     1     0%    /dev
tmpfs                                20480    228 20252     1%    /tmp
tmpfs                                32768    120 32648     0%    /var
# 

这样就能删除了，但是还是没有解决最一开始的问题，就是在一次启动后，无法再次安装，再安装就找不到硬盘，或者硬盘无法手工删除原来的zfs分区导致无法进行下一步。