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Re: [Xen-users] xvda vs lvm

Mark Williamson wrote:
Hi, I'm just wondering if there are any speed or stability differences
between running a system directly of a LVM partition versus a xvd

I'm a little confused about what you're asking, so I'll explain a few things and hopefully it'll help some. Please ask again if I'm not answering the questions you wanted.
I was mainly wondering about the speed issues involved in the two approaches. Since I didn't hear anything the first few days, I also asked on #xen where I was told that there isn't any performance overhead and that overloading the normal disk, say /dev/hda1, will be phased out in the future.

Thank you for your answer.

Kind regards,

disk = [ 'phy:/dev/LVM/root,xvda,w', ]

This exports /dev/LVM/root as the whole disk device /dev/xvda in the guest.

disk= [ 'phy:LVM/root,hda1,w',]

This exports /dev/LVM/root (as before) as the partition /dev/hda1 in the guest.

So, whether or not you include /dev in the device path, you're still exporting the same device.

As to whether to export a whole device or a partition...

Exporting as a single partition (e.g. /dev/hda1 in your example) has the advantage that /dev/LVM/root will be directly mountable in dom0 because it will not have been partitioned by the guest. The guest won't be allowed to repartition /dev/hda, it'll be stuck with one partition there.

Exporting as a whole device gives the guest flexibility to partition its VBD as it sees fit but means it's slightly less convenient to mount /dev/LVM/root in dom0 (but there are tools to read the partition and make this easy for you).

I usually go for the latter approach, but it doesn't matter in terms of speed and stability. It's really quest a question of administration convenience and how you want things to look like the guest.


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