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Re: [Xen-users] One Disk, multiple DomUs and Linux Swap

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] One Disk, multiple DomUs and Linux Swap
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Wed, 24 Jan 2007 18:31:49 +0000
Cc: Reinhard Brandstaedter <Reinhard.Brandstaedter@xxxxxx>
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> If I use one logical volume (with complete partition layout) as a
> read-only disk for multiple DomUs it works fine and I can start as many
> DomUs as I want, as long they don't write to the filesystems on that
> disk.

Correct.  dom0 can't write to it either, of course.

> But what is if this logical volume contains a swap partition? The swap
> partition is also shared between multiple DomUs and needs to be
> writeable. So it can't be a partition on the logical volume.

Sharing a swap partition between domUs is not going to work.  In fact it'll 
probably corrupt your virtual machines and crash them rather quickly, since 
they'll all be overwriting each other's swap data.

> I'd have to specify an extra disk device for each DomU which contains
> the swap partition, right?
> like 'phy:/dev/vm/test-swap-%d,xvda,r' %vmid

Best to avoid all possibility of them interfering with each other's swap 
space - otherwise it's a security problem as well as likely to crash. Giving 
them separate LVs as swap devices would be the most straightforward path 
here, I think.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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