Re: [Q] multi-disk

[Remco Blaakmeer <remco@blaakmeer.student.utwente.nl>]

On Thu, 20 Nov 1997, Vladislav Papayan x285 wrote:

> Hello,
> I have root partition on /dev/hda5
> /usr and /home directories on /dev/hdb1
> 
> I have another Harddisk I would like to put it
> such that it increases the space for my /usr and /home
> I compiled my kernel to include linear and Raid personalities
> for MD.  My question is: is it doable to mount my new disk
> in such a way that it increases transparently the space on 
> my /dev/hdb1 device?

Yes it can be done, but you will loose any data that is on /dev/hdb1 in
the process, so first make a _good_ backup.

To configure and use the MD driver you'll need the mdutils package. Use
mdcreate to create the /etc/mdtab file, like this:

# mdcreate -c8k raid0 /dev/md0 /dev/hdb1 /dev/hdc1

Then, 'start' the MD partition:

# mdadd -ar

Now you're set up and ready to use the device. The next action will
effectively destroy any filesystems that are on any of the partitions that
compose the md device:

# mke2fs /dev/md0

After this you can mount it like any other partition and start restoring
the system.

Things you should do *before* you do the above:

- read /usr/doc/mdutils/README.gz
- read the man page for mdcreate
- read the man page for mdadd
(and try to understand what they say)

Note that this will work with any number of partitions on any number of
disks. Just supply their names to the 'mdcreate' command. But if you're
looking for an increase of performance, I would recommend using one
partition on either /dev/hda or /dev/hdb and one partition on either
/dev/hdc or /dev/hdd. If you use two disks that are on the same IDE
controller, you will not get more performance. This is caused by the
design of the IDE bus.

Also note, that I did not test the command lines above. I checked the man
pages, but you should re-check them to see if they are really correct (but
you always do that, don't you?).

Last note: at bootup, the "mdadd -ar" command is automatically run when
/etc/mdtab exists (if you have a recent enough Debian system, you might
want to 'grep mdadd /etc/init.d/*'), so you don't have you worry about it.

Remco


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