Suggestions for working with unstable nvme dev names in AWS

[Matthew Seaman]

On 14/05/2019 03:35, George Hartzell wrote:
> Can anyone speak to the current state of device names for nvme disks
> on AWS using the FreeBSD 12 AMI's?  Is name-stability an issue?  If
> so, is there a work-around?
> 

I don't know about device name stability in AWS instances, but if you
are using ZFS, then shuffling the disks around should not make any
difference.  With physical hardware it should be possible to eg. pop the
disks out of one chassis and insert them into another in whatever order,
and the system will still boot correctly.  This sounds like the virtual
equivalent of that.

Technically, ZFS writes a label onto each disk which identifies it as
belonging to a zpool and its role within that zpool.  So long as the
system can interrogate the disk at boot time, it will work out.

If you're using UFS, or you have swap partitions separate to your ZFS
then definitely investigate labelling your partitions -- see glabel(8)
or gpart(8).  This allows you to label a partition as eg. 'root' and
then you can mount it by using the label as a device name eg.
/dev/gpt/root in fstab(5).

The FreeBSD installer defaults to using labelling like this both for ZFS
and UFS installs.

	Cheers,

	Matthew

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