[Sussex] Raid install

[Stephen Williams]

On Sat, 2005-09-10 at 06:00 +0100, Steve Dobson wrote:
> Dave
> 
> On Fri, Sep 09, 2005 at 11:18:06PM +0100, Dave Chapman wrote:
> > Are there any caveats for installing to a raid0 partition.
> > I believe that I will need a /boot and swap on a non raid drive.
> 
> You are correct.  The /boot partition (where your kernel lives)
> needs to be on a non-raid partition as the boot loader (grub 
> lilo) that is installed in you MBR one the boot partition is not
> raid aware.
> 

Alternatively, if you're only planning to use 2 disks in an array, you
can create an identical partition on each disk, set each type as linux
(83), use the partition on the first disk in the array as a standard
linux /boot partition, and set your BIOS to boot from the RAID device.
Any other partitions can be set to linux raid autodetect and used to
create the necessary RAID arrays.


> I'm not sure about this but I think swap can be on any device.
> The problem with running software raid is the the raid device
> must be set up before swap is mounted - much easier to make
> swap a native disk partition.

I run swap on RAID 1 arrays without a problem. If you compile MD support
into the kernel, the arrays are created automatically by the kernel and
are ready to go by the time swap is initialised.

>  
> > I'm not too bothered if the system crashes if a hard drive
> > fails thats why I have not mirrored the drives Just as long
> > as my /home survives. So thats on /dev/hdb

That's fine, but your system is at risk if either of the RAID 0 drives
fails. Effectively you have double the chance of a fatal disk error
occurring. I'd seriously think about using RAID 1 arrays here. If you
follow the setup above, you can copy the contents of /boot on RAID disk
0 to RAID disk 1, and use grub to setup the MBR of RAID disk 1 as well.
This means that in the event of a RAID disk 0 failure, you can set your
RAID disk 1 to be the boot disk and carry on as before. The advantage of
this is that when you get a new replacement disk, you can sync the new
disk to the existing one using the RAID controller's built in management
system.

> 
> Well a hard drive crash may happen to any disk.  If it happens
> to your /dev/hdb then you will loss your /home partition anyway.
> 
> If you were to mirror and mount /home on the mirrored partition
> then in order to lose /home *ALL* disks in the mirror would
> have to fail.
> 

Yup, I recommend RAID 1 for /home too.

Steve W.


> > PS
> > I will try to make the fair Sunday
> > For moral support but I'm working that night
> 
> All support is welcome.
> 
> Steve
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