Set default ext4 mount option commit=30 on cloud images

[Dimitri John Ledkov]

One of the defining features of linux-kvm kernel flavour is the bump of the default ext4 commit option from 5s to 30s in the ext4 kernel driver. This trades performance, with data-safety.

In order to consolidate kvm & generic kernel flavours I am seeking consensus to migrate this kernel patch, into a default change of the /etc/fstab option instead.

Specifically to at least explicitly set this option in fstab on our minimised images that use linux-kvm kernel.

Separately, I do believe this option should be set on all our cloud images - even those used on baremetal instances and/or preinstalled boards (raspberry-pi, risc-v etc) as this option will be especially useful on the under powered systems.

Reference:

https://docs.kernel.org/admin-guide/ext4.html

commit=nrsec (*)
This setting limits the maximum age of the running transaction to ‘nrsec’ seconds. The default value is 5 seconds. This means that if you lose your power, you will lose as much as the latest 5 seconds of metadata changes (your filesystem will not be damaged though, thanks to the journaling). This default value (or any low value) will hurt performance, but it’s good for data-safety. Setting it to 0 will have the same effect as leaving it at the default (5 seconds). Setting it to very large values will improve performance. Note that due to delayed allocation even older data can be lost on power failure since writeback of those data begins only after time set in /proc/sys/vm/dirty_expire_centisecs.

[Launchpad Janitor (janitor)]

This bug was fixed in the package livecd-rootfs - 2.804

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livecd-rootfs (2.804) lunar; urgency=medium

  * Clarified with Erich that edubuntu should install ubuntu-desktop-minimal
    task.

 -- Steve Langasek <email address hidden> Fri, 24 Feb 2023 21:11:56 -0800