Re: [linux-lvm] Ext3 -> ReiserFS on '/' conversion problem

[Madison Kelly <linux@alteeve.com>]

Thank you for such a lengthy responce, Holger.

	While I backup '/' to '/etc/sdd1' I have '/dev/sdd1' formatted as 
'ext3'. I will try making  custom kernel in the morning to be sure that 
ReiserFS is natively supported. I guess the biggest question in that 
last post I had was how can I force the OS to use the '/etc/sdd1' as the 
root partition instead of '/dev/vg0/root'? It isn't directly an LVM 
question though so I may have stepped out of bounds asking that one 
here... The joys of being new.

	As for extending the RAID array, I feared that what you said may be 
true. I am trying to build a storage platform that can (after going 
live) survive a disk failure and have space added without taking the 
partition off-line. I've read about the raid tools and I hoped that once 
I extended the RAID5 array (assuming I can do so, one disk at a time) I 
then wanted to pass the new space along to LVM... Am I attempting the 
impossible? :p

	Thank you again, everyone here is so helpful!

Madison

wopp@parplies.de wrote:
> Hi,
> 
> at some point in this thread, Madison Kelly wrote:
> 
>>I am still getting a kernel panic now but it no longer
>>seems to have anything to do with LVM, simply it is -still- looking for
>>an ext3 partition and obviously failing to find it.
> 
> 
> sorry to say so, but it never did have anything to do with LVM. Unless I
> completely misunderstood you, you first had / on LVM as ext3, and it worked.
> When you try to boot with / on /dev/sdd1 as reiserfs, it doesn't work.
> 
> It may sound obvious (and the thread has already come to this conclusion -
> I'm just trying to make it more clear), but your kernel doesn't support
> reiserfs, so you have to load reiserfs as a module from initrd - by whatever
> means Redhat provides or by manually creating an appropriate initrd (if you
> do that, use the one you have as a starting point). Or, of course, compile a
> kernel with reiserfs support built in.
> 
> You don't need to do any of this from the 'rescue disk' (especially not
> compile a kernel ;-). You can just as well boot into your normal setup (with
> / as ext3). If I'm not totally mistaken, the FS type of / is not specified
> anywhere but rather autodetected by the kernel on boot. Between booting into
> your ext3 system on /dev/vg0/root and your reiserfs copy on /dev/sdd1, you
> don't have to change any files. Come to think of it, how would the kernel
> use any file-based information to determine the type of the root FS? It would
> obviously need to mount / before reading the configuration, so once it can
> read it, it doesn't need it any more.
> And you can most probably tell GRUB what root device it is to pass to the
> kernel on its boot command line too [I don't use GRUB, so I can't tell you
> how] - or specify two alternative boot targets in the configuration file.
> 
> Concerning the 'df' output, 'df' takes its information from /etc/mtab, so if
> you put the line
> 
> /dev/ttyS0 / ext3 rw 0 0
> 
> in there, it may appear as though your first serial port were mounted on
> / :-). Nothing really seems to need to know where / physically resides, or
> if they do (LILO ...), they have better means of finding out [though I've
> never tried running 'lilo' with /boot as a part of / and the above entry in
> /etc/mtab :-]. This seems to result in not much effort being put into
> writing the correct root device name into /etc/mtab on boot (see the
> 'rootfs' output of 'df' on your 'rescue disk' - that simply means 'well,
> whatever it may be').
> 
> It IS sometimes confusing when you want to be 100% sure which disk you are
> operating on. It might help to go by the size reported by 'df', which should
> be accurate in any case.
> 
> 
>>Anyway, I am off to try converting again now that I know to try passing
>>"init=reiserfs" in grub (will it work though?... Off to see!)
> 
> 
> What would that do? Run 'reiserfs' [relative to the CWD, probably /] instead
> of /sbin/init after mounting the root FS? ;-)
> 
> 
> A remark on your original question:
> 
>>Am I on the right track?
> 
> 
> I don't think you'll be able to resize a software raid array and extend the
> PV. Can you create your array in degraded mode instead (with three data disks
> and the fourth one marked 'failed')? Then you'd have your spare disk for
> installation which you could later 'raidhotadd' to the array to get your
> parity information rebuilt. I don't think you're too worried about
> interruption of service during the installation ;-).
> I doubt a standard installation frontend supports this though, so you might
> need a bit of tweaking to get that to work.
> 
> Hope that helps in some way.
> 
> Holger