[NTLUG:Discuss] Software RAID using file "device"?

[Stuart Johnston]

Thanks, losetup was the piece I was missing.  I already used the symlink 
method on the server, which was probably easier anyway, but I went ahead 
and tested this out.

I created two loop-back devices and was able to use them with both mdadm 
and lvm.  However. my system hard-locked when trying to fill the mounted 
filesystem with files.  LVM seemed to work a little better, after only 
very limited testing.

Thanks,
Stuart

Robert Thompson wrote:
>>neither mdadm nor lvm seem to be willing to work with a non-block
>>device.
> 
> 
> Have you tried a loopback device (man mount and search for loop)? You
> can create a loopback mount from a file and attempt to use that.
> 
> After a quick search here are the commands you'll need:
> 
> Create a 50M file
> # dd if=/dev/urandom of=/tmp/test.img bs=1M count=50
> 
> Mount the file using the loopback tools
> # losetup /dev/loop0 /tmp/test.img
> 
> Create a filesystem on the device
> # mkfs -t ext3 /dev/loop0
> 
> Detach the file
> # losetup -d /dev/loop0
> 
> Mount the file as a device for use
> # mount /tmp/test.img /mnt -o loop=/dev/loop0
> 
> Redhat should have these commands installed and the kernel is already
> compiled for loopback device support. Do a man on any of the above
> commands for more details.
> 
> I've never tried setting up a loopback device with another drive for
> raid0 so let us know if you get it to work.
> 
> Robert Thompson
> 
> 
> On Thu, 2005-10-20 at 19:46 -0500, Stuart Johnston wrote:
> 
>>I have a server with two partitions, / and /home (not the best setup, I 
>>know).  The /home partition is coming very close to running out of disk 
>>space and I am trying to figure out a way to use some of the extra space 
>>on / without requiring a trip down to the data center.  This would only 
>>need to be a temporary solution.
>>
>>When I setup the system, I didn't worry too much about the partition 
>>setup because I was using LVM, which I thought would allow me to easily 
>>re-allocate the partitions as needed.  It turns out not to be quite so 
>>easy since you can't generally resize an ext3 partition while it is mounted.
>>
>>I was thinking about how in Linux, devices are treated like files and 
>>you can often use them interchangeably.  So, if I created a file on / 
>>then I could use it as a device in mdadm or lvm to combine linearly with 
>>the /home partition (which can be unmounted and resized remotely). 
>>Unfortuntately, neither mdadm nor lvm seem to be willing to work with a 
>>non-block device.
>>
>>Any suggestions on how to make this work?
>>
>>thanks,
>>Stuart Johnston
>>
>>_______________________________________________
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>>
> 
> 
> 
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