解决unable to find device node for dev ad4s1b in dev故障

昨天在一台比较老的机器上安装freebsd 8，结果分区完毕之后，在Commit步骤地时候，提示：
“Unable to find device node for /dev/ad4s1b in /dev!
The creation of filesystems will be aborted.”

看样子是硬盘的一些问题，我手头也没可用的额外的硬盘来测试，在google查阅了大量资料，众说纷纭吧，有说的DMA模式的问题，有说因为分区的时候不应该使用“W”，搞到凌晨 2点多，最后发现了这篇：http://www.pubbs.net/201002/freebsd/3072-80-install-fails-to-create-filesystem-quotunable-to-find-devicenodequot.html

发现其中Jeremy Chadwic兄弟的一段回复：

Jeremy Chadwick wrote:
>> Yes, ad0s1b is the swap, but I think it fails before doing newfs.
>> “Writing partition information to ad0” is the last message I see before
>> the error occurs, no newfs popups occur.
By the way, in the fixit console /dev has ad0b but not ad0s1b.
> Can you get this disk into a system (or the same system if booting off
> CD, etc.) where you can do the following to it and then retry the
> installation?
>
> dd if=/dev/zero of=/dev/ad0 bs=64k count=1
>
> No, this isn’t a joke. This should also clear up the GEOM label
> error/warning you see.

使用dd if=/dev/zero of=/dev/ad0 bs=64k count=1 把GEOM（geometry）标签清理掉。
我没BSD环境，就把硬盘挂到一台linux机器上作为第二块硬盘，执行：
# dd if=/dev/zero of=/dev/sdb bs=64k count=1
硬盘挂回去就OK了！