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QuantumMechanic
Asked: 2016-01-07 14:52:05 +0800 CST

Handling /etc/fstab when upgrading linode from Xen to KVM

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I have a linode that is currently on one of Linode's Xen servers. I see that I am eligible to upgrade to a KVM linode.

One thing that concerns me is that Linode's upgrade guide says block devices will change from the /dev/xvda naming scheme to the /dev/sda naming scheme.

My /etc/fstab is:

proc        /proc        proc    defaults                       0 0
/dev/xvda   /            ext3    noatime,errors=remount-ro      0 1
/dev/xvdb   none         swap    sw                             0 0

so I would think I am going to have to modify it in some way in conjunction with the upgrade.

Should I just edit the /dev/xvda and /dev/xvdb entries to /dev/sda and /dev/sdb before shutting down and upgrading?

Should I switch to the UUID= style of declaring devices? (Would the device UUID even stay the same, now that I think about it?)

I did open a support ticket with Linode and all they said was "turn on Distro Helper in your config profile before you upgrade and that should take care of it". Which leaves open the chance that it won't, so I'd prefer to do a known good thing proactively.

Relatedly, I assume the "root device" option in the configuration profile in the management UI (which is a dropdown that gives the /dev/xvdN options) will correctly map /dev/xvda to /dev/sda, etc. when you upgrade?

All in all, I'd love to hear from people who has put their linode through the Xen->KVM transition to see how this issue (and others I don't know about) shake out.

linux

1 Answers

  1. Best Answer

    You have no way of predicting what the device names or IDs will be after a significant hardware change (virtual hardware in this case, from Xen to KVM). Linode is the only entity here who knows what's going to change and how you should proceed if you upgrade.

    With that said, don't do this. You're forcing yourself to take an outage. If it breaks, you'll be on a support ticket with them until they sort out your issue. If you're lucky, you'll only lose time and not your data once it is done. A "known good thing" is to back up your Linode server's data and config, stand up a new KVM instance and migrate your data and services to the new host. If you cannot do this in about an hour using configuration management software, you are playing with fire. Furthermore, since you are a professional on a site for professionals, what on earth are you doing running servers without configuration management present?

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