[Gluster-devel] Open Shared Root GlusterFS Patches and HowTo

[Gordan Bobic]

Here's a preliminary version based on the OSR RHEL5 GFS mini-howto from 
here: 
http://www.open-sharedroot.org/documentation/rhel5-gfs-shared-root-mini-howto

Modified/added files are attached.

Prerequisites
-------------
Freshly installed RHEL5.

Install RHCS components:
# yum install cman

Install Com.oonics Packages
---------------------------

# yum install comoonics-bootimage \
		comoonics-cdsl-py \
		comoonics-bootimage-extras-glusterfs

[Note: I'm assuming the package for this will be called extras-glusterfs 
since that was what the DRBD one I submitted ended up being called.]

Install GlusterFS patched fuse packages:
# wget 
http://ftp.gluster.com/pub/gluster/glusterfs/fuse/fuse-2.7.3-2.src.rpm

# rpmbuild --rebuild fuse-2.7.3-2.src.rpm
# rpm -Uvh /usr/src/redhat/RPMS/x86_64/fuse-2.7.3-2.x86_64.rpm \
	/usr/src/redhat/RPMS/x86_64/fuse-libs-2.7.3-2.x86_64.rpm \
/usr/src/redhat/RPMS/x86_64/fuse-kernel-module-2.6.18-92.1.22.el5-2.7.3-2.x86_64.rpm

# wget 
http://ftp.gluster.com/pub/gluster/glusterfs/2.0/2.0.0/glusterfs-2.0.0rc1.tar.gz

# rpmbuild -tb glusterfs-2.0.0rc1.tar.gz
# rpm -Uvh /usr/src/redhat/RPMS/x86_64/glusterfs-2.0.0rc1-1.x86_64.rpm

[Note: The current versions may change, the ones listed are correct at 
the time of writing this document. The paths above also assume x86-64 
architecture.]

Create a cluster configuration file /etc/cluster/cluster.conf with the 
com_info tags. This time fencing isn't mandatory if you aren't using 
resource failover, as unline GFS, GlusterFS won't block if a peer goes 
away. For GlusterFS splitbrain caveats and handling see 
http://www.gluster.org/

[cluster.conf attached]

A quick note about the disk layout of the underlying disk. This howto 
assumes the following:
/dev/sda1 /boot
/dev/sda2 /
/dev/sda3 swap
/dev/sda4 comoonics-chroot (so we can deallocate the initrd)

On /, we are assumed to have a directory /gluster/root which contains 
the gluster rootfs.

Create the GlusterFS root volume specification in 
/etc/glusterfs/root.vol. Here is an example of a simple volume spec file 
for a 2-server AFR (mirroring) configuration where each server has a 
local copy of the data. Note that you could also do this diskless, with 
the rootfs being on remote server(s) much like NFS, and even distributed 
or striped across multiple servers. See GlusterFS documentation for details.

[root.vol attached]

Mount the glusterfs file system:
# mkdir /mnt/newroot
# mount -t glusterfs /etc/glusterfs/root.vom /mnt/newroot

Copy all data from the local installed RHEL5 root filesystem to the 
shared root filesystem:

[ ... the rest of the section is identical to the GFS howto ... ]

Make sure you apply the patches from 
/opt/atix/comoonics-bootimage/patches to the init scripts in the new 
root, especially the network and halt init scripts!

Note that the RPM library in it's default configuration WILL NOT work 
under GlusterFS. GlusterFS is fuse based and thus doesn't support 
writable mmap(), which BerkeleyDB (default RPM database format) requires 
to function. To work around this problem, we can convert the RPM 
database to use SQLite. The functionality is already built into RHEL5 
RPM packages, we just need to do the following:


# rpm -v --rebuilddbapi 4 --dbpath /var/lib/rpm --rebuilddb

and then change the following lines in /usr/lib/rpm/macros:
%_dbapi 3
%_dbapi_rebuild 3

to

%_dbapi 4
%_dbapi_rebuild 4

[Note: This should _probably_ be another patch in 
/opt/atix/comoonics-bootimage/patches, trivial as it may be.]

[Note: Updated network.patch attached, the current one in the repo 
didn't seem to apply cleanly, and I added the exclusion of network 
disconnection when GlusterFS is used.]

[Note: You cannot use a GlusterFS based shared boot per se, but you 
COULD use GlusterFS to keep /boot in sync and boot off it's backing 
storage device. No new devices need be created, only an additional 
volume spec using the /boot volume as the backing store for GlusterFS. 
All operations on top of GlusterFS would cause the /boot device to get 
mirrored across the machines. This is only meaningful with 
AFR/mirroring. Also note that grub is virtually guaranteed to get 
horribly confused when asked to make a GlusterFS based file system 
bootable. In conclusion - don't do this unless you understand what I'm 
talking about here and know what you're doing.]

Create the shared root initrd as per usual:

/opt/atix/comoonics-bootimage/mkinitrd -f 
/mnt/newroot/boot/initrd_sr-$(uname -r).img $(uname -r)


Final note: You can side-step the copying of the root FS by operating 
directly on the master copy. This means you won't have to then manually 
go and delete the initial installation (except for the /gluster 
directory), but it also means that any mistakes along the way will 
render the system unusable and you'll have to re-install from scratch 
and try again. You would then, of course, need to change the path in 
root.vol from /mnt/tmproot/glusterfs/root to /mnt/tmproot.

Awaiting peer review. :)

Gordan
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