Re: [Xen-users] why errors happen when two vms start concurrently ?

[Grant McWilliams <grantmasterflash@xxxxxxxxx>]

On Wed, Dec 21, 2011 at 9:55 PM, Bryant Kobe <shijie1234321@xxxxxxxxx> wrote:

hello, Grant ,

other vms can also be started after these two errors occurred inÂ

my server , even the vm just error happened can also be startedÂ

if you reexecute " xm start *** ".Â

I have printed many logs in xend source code , but find no implies.

I've no idea what the next direction I should go to solve the problem.Â

I don't want to change my system .

Bryant

It was always my theory that there should be some locking somewhere but it isn't there. For instance if you start two VMs and both access the same resource at the same time one tramples on the other.ÂÂThis was just a gut feeling though. It just seemed that xm needed to lock the resources when creating the disk/net interfaces then releasing it so the next process could have it. Again I worked around it after fighting it for months. I found that for the first 15 VMs they'd all start fine but after that the system would start to really slow down (since a lot of VMs are hitting their disks at the same time) and the errors would start. If I started them slowly one at a time they worked fine. It seems that this problem happens right at the beginning of the xm create process.

Moving to LVM for disks did improve it for me. Again I'd guess that it's just because the process needed to use an LV is a lot shorter than to create a tapdisk to access a file.

Grant McWilliams

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