Software RAID1

[Marius Gedminas]

On Fri, Aug 17, 2007 at 10:16:21AM -0800, Damien Hull wrote:
> Here's what I have:
> 
>     * Edubuntu 7.04 with updates
>     * Intel motherboard
>     * Two SATA drives of the same size
>     * SWAP is not on RIAD
>           o Each drive has a swap partition
>     * Software RAID1
>           o /
>           o /home

I have a similar situation, only with Ubuntu 5.10 (shame on me for not
upgrading).

> GRUB questions:
> 
>    1. How do I install GRUB on sdb?

grub-install /dev/sdb, probably.

I use LILO, because it supports RAID-1, and debugging GRUB failures over
the phone was too difficult (the server is in a data centre a thousand
kilometers from where I am).

>    2. How do I configure grub to boot even if one drive is missing or
>       not working?
>          1. Example: sda goes bad. Need to boot from sdb

If sda is missing your sdb becomes your sda and everything works fine,
since they're identical.  I don't know what would happen if you had a
sda but couldn't read the boot loader from it.  Probably you'd need to
do some manual kicking from the console, or pull out the bad disk.

Failures in other partitions aren't problematic.

> SWAP questions:
> 
>     I'm not sure how this works but I read somewhere that swap should
>     not be on a RAID partition. Some edititing of /etc/fstab needs to be
>     done. Can someone tell me what goes in there?

I have this:

/dev/sda4       swap            swap    pri=1                   0       0
/dev/sdb4       swap            swap    pri=1                   0       0

When you specify the same priority, the kernel uses both disks equally.

> Here's what should happen:
> 
>    1. If a drive fails the system should continue to run

It does (I've seen quite a few failures).  RAID goes into degraded mode,
and a cron script emails root the contents of /proc/mdstat.

I suppose if a bad block appeared in the middle of a swap partition, the
system could crash.

>    2. If the system is rebooted the good drive should boot
> 
> This is assuming that everything is configured correctly.

Marius Gedminas
-- 
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