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Re: A / with XFS on RAID5 with an external log

To: Adam Sjøgren <asjo@xxxxxxxxxxxx>
Subject: Re: A / with XFS on RAID5 with an external log
From: Steve Lord <lord@xxxxxxx>
Date: 11 Mar 2002 16:24:31 -0600
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <87sn76kbep.fsf@xxxxxxxxxxxxxxxxxxx>
References: <87sn76kbep.fsf@xxxxxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Mon, 2002-03-11 at 16:05, Adam Sjøgren wrote:
>   Hi.
> This is my first post to the mailinglist, so I hope you'll bear with
> me. I've spent quite some time spent the last four days searching,
> reading, experimenting trying to find the solution to the following
> question:
> I'm experimenting on a box with three disks with having a root
> filesystem on XFS on RAID5. I'm having problems booting Linux if I
> have an external log (as recommended in the faq). I've tried with
> 2.4.18 with the 2.4.18-patch from the ftp-server and with 2.4.14 with
> the 1.0.2 patch as distributed by Debian.
> My setup is three identical disks that look like this:
>  hda1 small /boot
>  hda2 raid1 for the log (md1)
>  hda3 swap/temporary ext2fs-root while experimenting
>  hda4 raid5 for my xfs-/ (md0)
> Now, I 'mkfs.xfs -l logdev=/dev/md1 /dev/md0', and the fs is
> created. I can mount it with 'mount -o logdev=/dev/md1 /dev/md0 /mnt'
> and copy stuff to it. That's all fine.
> But when I configure lilo to use /dev/md0 as root and reboot, I can't
> make it work. I have different scenarios depending on what I try:
>  *) Without initrd and no options: Linux boots and gets to the
>     point where it tries to mount / - it then says that xfs needs a
>     logdev-option to mount the partition, and the kernel panics.
>  *) Without initrd and passing LILO linux rootflags=logdev=/dev/md1:
>     Linux boots, EXT2fs complains that it doesn't know what to do with
>     logdev, and I get a kernel oops (when XFS tries to mount?)
>  *) Without initrd and passing LILO linux rootflags="logdev=/dev/md1"
>     (wrong format for option): Linux boots, EXT2fs complains about
>     "log, XFS complains about "log - the root fs isn't mounted, and
>     the kernel panics.
>  *) If I build the kernel with initrd and tell lilo to use it, XFS
>     complains about the lacking logdev-option. I've searched and read
>     and it seems to me that it should be extremely simple to make an
>     initrd that mounts /dev/md0 as / with logdev=/dev/md1, but none of
>     the stuff I've found has been "cookbook" enough to give me a clue
>     about how.
> I'm using Debians kernel-package' make-kpkg (with/without --initrd) to
> build a kernel-image-package which I then install.
> If someone could point me in the right direction, I'd be very happy.
> I don't want to install a lot of stuff on an xfs-filesystem with an
> internal log (which I _can_ get Linux to mount when booting, it's not
> all misery :-)) when/if I can't (easily) change from internal to
> external later on...
>   Best regards,
>     Adam.

Two things to mention.

 o first of all we are testing code which should help with the internal
   log performance of raid5 - but it is not ready now.

 o second maybe you need two boot options here:
        rootfstype=xfs and rootflags=logdev=/dev/md1

If I read the code correctly, this should make it only try and use



Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@xxxxxxx

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