Re: Software raid OK?

[Sam Kuper <sam.kuper@uclmail.net>]

Michael,

2009/4/20 Michael Iatrou <m.iatrou@freemail.gr>

When the date was Monday 20 April 2009, Douglas A. Tutty wrote:

> On Mon, Apr 20, 2009 at 03:29:00PM +0300, Michael Iatrou wrote:
> > There is no particularly good reason to have the swap on RAID. You
> > should define three independed swap partitions; if disk fails, kernel
> > will use the other available.
>
> If swap fails, what happens if something important to the running of the
> system (not just a user app) is swapped-out?  I've seen advice on this
> list many times that to avoid a crash, if other system stuff is on raid,
> that swap should be as well.

I cannot confirm that; instead I am assuming a workflow like the following:

1. A disk is about to fail
2. Notification from SMART hits sysadmin's mailbox
3. # swapoff /dev/sdXY
4. Replace disk, create partitions
5. # swapon /dev/sdXY
6. # mdadm /dev/mdK -a /dev/sdXZ

If the system is running unattended - for instance if it's a server being run by a hobbyist, which doesn't have a sysadmin permanently available to respond to problems - then step 3 may not occur before the disk fails. In this scenario, isn't Douglas right that it's better to have the swap on (redundant) RAID?

Many thanks,

Sam