negative free blocks after mirror! [was: Re: mirror without destroying existing contents]

[Steve Franks]

On 3/17/07, Jonathan McKeown <jonathan at hst.org.za> wrote:
> On Friday 16 March 2007 21:48, Steve Franks wrote:
> > On 3/16/07, John Nielsen <lists at jnielsen.net> wrote:
> > > On Friday 16 March 2007 11:18, Steve Franks wrote:
> > > > I get the following:
> > > >
> > > > #gmirror label -v -b split -s 1024 data ad0
> > > > can't store metadata on ad0: operation not permitted.
> > >
> > > That most likely means that you currently have a filesystem on ad0
> > > mounted. If that's the case you should be glad that the OS was smarter
> > > than you. What steps had you taken prior to this?
> >
> > It appears to say in the manpage that you can do this on a disk with
> > an existing filesys - would you expect it to work if the disk is
> > unmounted first, then?
>
> The way to do this is potentially a little risky but I haven't had a problem
> with it yet after setting up several mirrors on live fileservers. There is a
> sysctl called kern.geom.debugflags: if you set this to 16 it will allow you
> to change the mounted filesystem. Bear in mind that since the metadata for
> the mirror is written to the last sector of the disk, there is a small risk
> of data loss: if that sector contains data it will be overwritten.
>
> There's a thorough howto by Ralph Engelschall, and an OnLamp article by Dru
> Lavigne, with more details:
>
> http://people.freebsd.org/~rse/mirror/
> http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html
>
> Jonathan
>

Yes, the origonal disk was pretty full, but, I suspect this is not a good thing:

Filesystem              1K-blocks      Used     Avail Capacity  Mounted on
/dev/ad0s1a                507630     95254    371766    20%    /
devfs                           1         1         0   100%    /dev
/dev/ad0s1e                507630     30688    436332     7%    /tmp
/dev/ad0s1f             152451398   5956408 134298880     4%    /usr
/dev/ad0s1d               1444526    103600   1225364     8%    /var
/dev/mirror/rainstones1 151368706 141135278  -1876068   101%    /rainstone

How is that even possible?

Steve