Transferring the root filesystem to a ramdisk?

[Cordula's Web]

Hello,

in an attempt to save power on FreeBSD servers, I'm
trying to replace the hdd with a ramdisk. The idea is to:

  1. boot from the hdd (or netboot from an NFS server)
  2. configure a ram disk (md(4))
  3. copy everything that's needed to ram disk
  4. transfer kernel root to ramdisk (*)
  5. turn off the hdd (**)

(*) is the hairy question.
(**) How can that be done?

I won't need paging, because there'll be enough ram for
everything (ramdisk, kernel and userland).

Now the questions are:

  * How to "attach" the root filesystem to the ram disk?

    Can this be done only through pxe/netboot before the
    kernel starts, or is there some kind of system call
    that can transfer root on a running system?

  * How to power off (and on) the hdd (both for ATA and SCSI)?

  * Will the power consumption decrease (no hdd) or will
    it increase (more ram)? Anybody measured this before
    with regular diskless machines?

Thanks,
-cpghost.

-- 
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