Re: HELP! Re: How to fix I/O errors? (SOLVED)

[Marc Auslander <marcslists@gmail.com>]

Marc Shapiro <marcnshap@gmail.com> writes:

> the past couple of weeks.  AIUI you can use LVM over raid.  Is there
> any actual advantage to this?  I was trying to determine the
> advantages of using straight raid, straight LVM, or LVM over raid.  If
> I decide, later, to use raid, how dificult is it to add to a currently
> running system (with, or without LVM)?
>
>
> Marc
I do not use LVM over raid 1.  I think it can be made to work,
although IIRC booting from an LVM over RAID partion has caused issues.

LVM is useful when space requirements are changing over time and the
ability to add additional disks and grow logical partions is needed.
In my case, that isn't an issue.  I have only a small number of
paritions - 3 because of history but starting from scratch, I'd only
have two - root (including boot) and /home.

I converted to mdamd raid as follows, IIRC.

Install the second disk, and parition it the way I wanted.
Create a one disk raid 1 partion in each of the new paritions.
Take down my system, boot a live system from CD, and use a reliable
copy program like rsync to copy each of the partitions contents to the
equivalent raid partition.
Run grub to set the new disk as bootable.  This is by far the
trickiest part.
Boot the new system and verify it's happy.
Repartion the now spare disk to match the new one if necessary.
You may need to zero the front of each partion with dd if=/dev/zero
to avoid mdadm error checks.
Add the partitions from that disk to the mdadm paritions and let mdadm
do its thing.