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Date:      Thu, 24 Mar 2005 10:51:04 -0500
From:      Bob Johnson <bob89@eng.ufl.edu>
To:        Odhiambo Washington <wash@wananchi.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: RFC 2005 - mounting two slices from 2 different disks to same mount	point ;)
Message-ID:  <4242E1E8.1090602@eng.ufl.edu>
In-Reply-To: <20050324151935.GA10374@ns2.wananchi.com>
References:  <20050324151935.GA10374@ns2.wananchi.com>

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Odhiambo Washington wrote:

>Hello Gang!
>
>On FreeBSD 5.3-RELEASE, we have mounted slices as follows:
>
>-bash-2.05b$ mount
>/dev/ad0s3a on / (ufs, local)
>devfs on /dev (devfs, local)
>/dev/ad0s3e on /tmp (ufs, local, soft-updates)
>/dev/ad0s3f on /usr (ufs, local, soft-updates)
>/dev/ad0s3d on /var (ufs, local, soft-updates)
>devfs on /var/named/dev (devfs, local)
>/dev/ad0s5 on /drive_d (msdosfs, local)
>/dev/ad3s1d on /tmp (ufs, local, soft-updates)
>
>
>/dev/ad0s3e was 500MB
>/dev/ad3s1d was 40GB
>
>In /etc/fstab, we specified the mount point for both to /tmp.
>
>We then wrote a 1GB file to /tmp and there was no error. The
>file was successfully written.
>
>Can an expert with disks tell me where the file was written?
>How did the system decide where to write the file? How did it
>"select" /tmp in this case?
>
>  
>
It was written to the last disk you mounted.  When you mount a disk, it
replaces whatever was mounted there previously.  At least, that's what
the mount docs say, I didn't actually try to test it.  If you do a df it 
should
show that /tmp has the capacity of the last drive you mounted there. 
Try mounting the 40GB drive first and then the 500 MB drive and
run your test again.

>Linux guys have talked about "disk spanning" using the method
>we just tested. I am wondering the dangers I face doing such
>a thing!!
>
>  
>
If you want to span disks, take a look at gconcat(8) or vinum(8).  gconcat
replaces an older utility I don't remember the name of at the moment.

>Happy Easter to ye all!!
>
>
>-Wash
>  
>

- Bob



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