[dm-devel] Is thin provisioning still experimental?

[Mike Snitzer]

On Mon, Jul 23 2018 at  1:06am -0400,
Drew Hastings <dhastings at crucialwebhost.com> wrote:

>    I love all of the work you guys do @dm-devel . Thanks for taking the time
>    to read this.
>    I would like to use thin provisioning targets in production, but it's hard
>    to ignore the warning in the documentation. It seems like, with an
>    understanding of how thin provisioning works, it should be safe to use.

It is stale.  I just committed this update that'll go upstream for the
4.19 merge window, see:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.19&id=f88a3f746ff0047c92e8312646247b08264daf35

>    If the metadata and data device for the thin pool have enough space and
>    are both error free, the kernel has plenty of free RAM, block sizes are
>    set large enough to never run into performance issues (64 MiB), all of the
>    underlying hardware is redundant on high performance NVME (no worries of
>    fragmentation of data volume)... is it still unsafe for production? If so,
>    can you shed some light on why that is?

It is safe.  You do just want to make sure to not run out of space.  We
now handle that event favorably but it is best to tempt fate.  No idea
what, if any, filesystem you intend to run but XFS has the ability to
discontinue retries for certain error conditions.  I highly recommend
you enable that for ENOSPC, otherwise you _will_ see the kernel block
indefinitely in XFS if thinp runs out of space underneath XFS.

>    Thin provisioning is so cool. It would be a shame to not use it!
>    Thank you so much!

Enjoy.

Mike