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

[Chris Cox]

Stuart Johnston wrote:
> Drew Myers wrote:
>> * Stuart Johnston (saj at thecommune.net) 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?
>>
>>
>> What OS are you running?  In RHEL4 you can use the ext2online utility to
>> resize the FS while it's mounted.
> 
> ext2online will only expand, not shrink a mounted fs.  Thanks for the
> suggestion though.  I didn't know RHEL4 (which this server is in fact
> running) had that kernel patch.

Also.. it implies growing the partition.  Sounds like LVM was not
used... so unless you can shrink whatever and grab contiguous space next
to the partition, you can't resize the parition.. and so you can't
grow the filesystem.

I think the symlink idea is the the best approach.

Use LVM next time and create a volume group for the OS and
a volume group for your user data.  Leave some room for
growing the OS areas.

Also.. I'm not sure ext2online will grow a mounted root filesystem...
can someone verify that?