Suggestions for working with unstable nvme dev names in AWS

[George Hartzell]

Matthew Seaman writes:
 > 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.
 > [...]

Thanks for the response!

Yes, once I have them set up (ZFS or labeled), it doesn't matter what
device names they end up having.  For now I just do the setup by hand,
poking around a bit.  Same trick in the Linux world, you end up
referring to them by their UUID or ....

The tricky bit is the automated setup.  Say I ask for two additional
devices, "this" and "that".  I intend to use "this" for high
performance what-cha-macallit so I specify high IOPS and etc....  I
intend to use "that" for less important stuff, so I specify "lower"
performance.

Now as the machine's provisioning itself (e.g. Ansible), how can I
reliably decide which to `zpool create` or `glabel` or ... with which
names?

The Linux world worked around this with the `udev` rules and *etc*
that I described earlier.

There are hacky ways to work around it, I could ensure that they're
different sizes and use that to decide.  I could do it in two stages.
*etc...*

I'm just wondering if there's a way to leverage the bit of info AWS
has tucked away for us.

g.