Transferring the root filesystem to a ramdisk?

[Julian Elischer]

On Sat, 31 Jan 2004, Bjorn Eikeland wrote:

> I'm probably in over my head here, but;
> chroot should change the root filesystem for you.
> (look in the manpages for more details)
> 
> As for powering down the hdd I did find a page for this,
> but havent had time to play with it yet:
> http://www.cran.org.uk/bruce/software.php

there is a port "ataidle" that sets teh IDE drive's internal idle
timeout timer so it will spin down if you dont use it..

as for scsi, you can sent it a spin-down command with camcontrol but I
forget the actual command..
(it should be in the scsi .h files)

julian

> 
> best of luck!
> 
> > 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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