[openstack-dev] [nova] - Revert change of default ephemeral fs to ext4

Day, Phil philip.day at hp.com
Mon Dec 30 11:25:44 UTC 2013

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-------- Original message --------
From: Pádraig Brady <P at draigBrady.com>
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
Cc: "Day, Phil" <philip.day at hp.com>
Subject: Re: [openstack-dev] [nova] - Revert change of default ephemeral fs to ext4

> -          It causes inconsistent behaviour in the system, as any existing "default" backing files will have ext3 in them, so a VM will now get either ext3 or 3ext4 depending on whether the host they get created on already has a backing file of the required size or not.   I don't think the existing design ever considered the default FS changing - maybe we shouldn’t have files that include "default" as the file system type if it can change over time, and the name should always reflect the FS type.

 > I'm not sure this is a practical issue since ephemeral storage is built up from blank by each instance

Maybe it varies by hypervisor; my understanding is that at least in libvirt the ephemeral disks are cow layers on a shared common backing file that has the file system in it.  The naming convention includes the size and fs type or "default" and is only created once per size-fs combination.

So this is a real issue - I think that maybe the eventual change to ext4 need to be combined withoving away from "default"  in the file name.


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