Re: Converting ext3 to RAID1 ...

Greetings ...

 Thanks for the reply ...  I was a little verbose with my first mail,
and was thinking that was why I did not get a response ...

2009/8/25 John Robinson [off-list ref]:

On Mon, 24 August, 2009 10:24 pm, Clinton Lee Taylor wrote:

quoted

http://www.issociate.de/board/post/498227/Ext3_convert_to_RAID1_....html

Wanting to convert an already created and populated ext3 filesystem.

I unmounted the filesystem, ran e2fsck -f /dev/sdb1 to check that the
current filesystem had no errors.
Then ran mdadm --create /dev/md0 --level=1 -n 1 /dev/sdb1 --force to
create the RAID1 device, answered yes to the question.

This rang alarm bells for me, so I checked your link above, and apparently
you shrunk the filesystem before doing this. If you shrink the filesystem,
and use a metadata version that puts the metadata at the end - as you did
by default in this case using version 0.90 - then your method is fine and
quite safe. If you don't shrink the filesystem, which you didn't mention
here, you'd be asking for a world of pain.

 mdadm did complain about size issues, so I did the shrink before
doing the rest of the procedure, so it seems a little safe ... Is the
metadata only in one place?  I know that a few superblocks are made in
the ext3 filesystem, for backup and speed ... Could mdadm or another
util made to be smart enough to move data out of it's way when do a
conversion like this?

Another surer method (making no assumptions about metadata version) when
you've two identically-sized partitions, the original and the new mirror,
is to mdadm --create /dev/mdX --level=1 -n 1 /dev/secondpartition ; mkfs
-t Y /dev/mdX ; mount -t Y /dev/mdX /scratch ; mount -o remount,ro /path ;
cp -a /path/* /scratch ; umount /scratch ; sed -i~ -e
's?/dev/originalpartition?/dev/mdX?' /etc/fstab ; umount /path ; mount
/path ; mdadm -add /dev/mdX /dev/originalpartition

That's slightly more like what the wiki article suggests, but still not
enough for your root filesystem or booting; they're being properly
exhaustive on converting from a 1-drive system to a 2-drive RAIDed one,
making sure you've no assumptions (apart from it being CentOS 5), it works
for your root filesystem and makes sure you end up with both drives
bootable.

 But the above method, wiki article and quite a few other links on the
internet, really go through the whole copy process and then adding the
extra drive, which really means keeping the system down for quite some
time.  I believe it to be the more recognized method, but the simple
procedure that I have used, seems quicker.

 I'm hoping to make a simple script that might be able to go through
the process, with warnings, tests and corner cases issues awareness
added, plus, with this as general knowledge, maybe mdadm would either
do the right thing every time or not be updated to kill a filesystem
when this process used ...

Thanks
Mailed
LeeT