Hi Stephen,

I'm writing you (referenced in [2] in  the description above) to enquire about the use of direct-lvm and overlayfs in the docker storage setup, as it pertains to AH 7.2.  As preliminary research, i've briefly read:

 http://developerblog.redhat.com/2014/09/30/overview-storage-scalability-docker/

Could you please comment on its accuracy?

Hi,

(In reply to Thien-Thi Nguyen from comment #2)

> I'm writing you (referenced in [2] in  the description above) to enquire
> about the use of direct-lvm and overlayfs in the docker storage setup, as it
> pertains to AH 7.2.  As preliminary research, i've briefly read:
> 
>  http://developerblog.redhat.com/2014/09/30/overview-storage-scalability-
> docker/
> 
> Could you please comment on its accuracy?

It is not exactly inaccurate, just old --- over a year old, which qualifies as ancient in docker years!  overlayfs was not available for us at the time that was written --- it's new in 7.2.

Can you work with the docker-storage-setup maintainer, Vivek Goyal, for info here?  I'm adding him to the BZ.  Thanks!

Thein,

The article you referenced is more about comparing performance of various storage backends. 

Following is the article which should be referenced to figure out how to configure storage for docker on rhel as well as atomic host.

https://access.redhat.com/articles/1492923

This article already has details about how to configure lvm thin pool. We need to add details of how to configure overlay.

Yoana Ruseva <yruseva> is already looking into adding overlay details to the article.

Related BZs (both assigned to yruseva): 1249168, 1267555

Per meeting w/ yruseva, we have partitioned the work:
- yruseva to document how to enable overlayfs for docker in various ways
- tnguyen to document an overview of overlayfs advantages (why use it?)

(In reply to Vivek Goyal from comment #4)

> [see] https://access.redhat.com/articles/1492923
>
> Yoana Ruseva <yruseva> is already looking into adding overlay
> details to the article.

Great.  Thanks for the pointer.  (BTW, please spell my name as "Thien-Thi".  Spelling it "Thein" is like spelling your name "Viev", both incorrect in vowel order and incomplete.)

I gather that both LVM thin pool and OverlayFS do the "usual" copy-on-write magic.  However, the primary feature that recommends OverlayFS over LVM thin pool is its support for page-cache sharing between snapshot volumes.
 (a) Is that correct?
 (b) Are there other compelling reasons to use OverlayFS over LVM thin pool?

Thanks again for your help in this documentation effort.

Here it is:

- https://access.qa.redhat.com/documentation/en/red-hat-enterprise-linux-atomic-host/version-7/getting-started-with-containers/#overlayfs_support
- https://gitlab.cee.redhat.com/rhel-atomic-host-documentation/atomic-host-content/blob/master/getting_started_with_containers/content/managing_storage_docker_formatted_containers.adoc

(The second link is in case the first does not work -- you will need to log in w/ kerberos.)

Overall section 8.6 looks good. Some brief comments.

8.6. OverlayFS support

#comment: Instead of OverlayFS support, will it be better to call it just
 "Overlay Graph Driver"

OverlayFS is a copy-on-write union file system that features page-cache sharing between snapshot volumes. Similarly to LVM thin pool, OverlayFS supports efficient storage of image layers. However, compared to LVM thin pool, container creation and destruction with OverlayFS uses less memory and is more performant. 

#comment: Above talks about only the pros and has not specified any downside of
 of using overlayfs. I think it is important to mention that overlayfs is
very new, does not support selinux yet and some of the file systems semantics
are different from standard filesystmes like ext4 and xfs. Hence one needs to
run their applications with overlayfs and make sure applications are fine with some of the new behavior. Following is a link to the non-standardard behavior of overlayfs.

https://github.com/torvalds/linux/blob/master/Documentation/filesystems/overlayfs.txt#L179

Thanks Vivek.  The intro blurb has been updated (see above for links) per your suggestions.  WDYT?

Looks good to me. Thanks.

ok: https://access.redhat.com/documentation/en/red-hat-enterprise-linux-atomic-host/7/getting-started-with-containers/chapter-8-managing-storage-with-docker-formatted-containers
Moving to CLOSED CURRENTRELEASE.