Gluster logo The last week of January and the first week of February were packed with events and meetings.

This blog contains my observations, opinions, and ideas in the hope that they will be useful or at least interesting for some.

CentOS Dojo in Brussels

The day before FOSDEM starts, the CentOS project organizes a community meetup in the form of their Dojos at an IBM office in Brussels. Because Gluster is participating in the CentOS Storage SIG (special interest group), I was asked to present something. My talk had a good participation, asking about different aspects of the goals that the Storage SIG has.

Many people are interested in the Storage SIG, mainly other SIGs that would like to consume the packages getting produced. There is also increasing interest from upcoming architectures to get Gluster running on their new hardware (Aarch64 and ppc64le). The CentOS team is working on getting the hardware in the build infrastructure and testing environment, the Gluster packages will be one of the first SIG projects going to use that.

The CentOS team maintains a Gluster environment for virtual machines. It is possible for CentOS projects to request a VM, and this VM will be located on their OpenNebula "cloud" backed by Gluster. This is a small environment with four servers, connected over Infiniband. Gluster is setup to use IPoIB, not using its native RDMA support. Currently, this is running glusterfs-3.6 with a two-way replica, OpenNebula runs the VMs over QEMU+libgfapi. In the future, this will most likely be replaced by a similar setup based on oVirt.

FOSDEM 2016

At FOSDEM, we had a very minimal booth/table. The 500 stickers that Amye Scavarda brought and a bunch of ball pens imported by Humble and Kaushal were handed out around noon on the second day. Lots of people were aware of Gluster and many were not. We definitely need a better presence next year, visitors should easily see that Gluster is about storage and not only the good-looking ant. Kaushal and Humble wrote detailed blog posts about FOSDEM already.

Some users that knew about Gluster also had some questions about Ceph. I unfortunately could not point them to a booth where experts were hanging around. It would really be nice to have some Ceph people manning a (maybe even shared) table. Interested users should get good advice on picking the best storage solution for their needs, and of course we would like then to try Gluster or Ceph in the first place. A good suggestion for users is important to prevent disappointment and possibly negative promotion.

The talk I gave at FOSDEM attracted (a guestimated) 400-500 people. The auditorium was huge, but "only" filled somewhere between 25-50% with a lot of people arriving late, and some leaving a few minutes early. After the talk, there were a lot of questions and we asked to move the group of people to a little more remote location so that the next presentation could start without the background noise. Kaleb helped in answering some of the visitors questions, and we directed a few to the guys at the Gluster booth as well. The talk seemed to have gone well, and I got a request to present something at the next NLUUG conference.

Gluster Developer Gatherings, Red Hat, Brno

This was mainly informal chats about different topics. We encouraged each topic to add a link to an etherpad where notes are kept. The presenters of the sessions are expected to send a summary based on the notes to the (community) mailing lists, which I won't cover here.

Some notes that I made during conversations that were not really planned:

  • Richacl needed for multiprotocol support, Rajesh will post his work-in-progress patches to Gerrit so that others can continue with his start and get it in for glusterfs-3.8. (Michael Adam)

  • QE will push downstream helper libraries for testing with distaf to the upstream distaf framework repo or upstream tests repo. MS and Jonathan are the main contacts for defining and enforcing an "upstream first" process. "Secret sauce" tests will not become part of upstream (like some performance things), but all basic functionality should. At the moment we only catch basic functionality problems downstream, when we test upstream we should find them earlier and have more time to fix them, less chance in slipping release dates.

    Downstream QA will ultimately consist out of running the upstream distaf framework, upstream tests repo and downstream tests repo.

  • Paolo Bonzini (KVM maintainer) and Kevin Wolf (QEMU/block maintainer) are interested in improved Gluster support in QEMU. Not only SEEK_DATA/SEEK_HOLE would be nice, but also something that makes it possible to detect "allocated but zero-filled." lseek() can not detect this yet, it might be a suitable topic for discussion during LSF/MM in April.

    One of the things that the libvirt team (requested by oVirt/RHEV) asked about was support for "backup-volfile-server" support. This was a question from Doron Fediuck at FOSDEM as well. It was the first time I heard about it. Adding this seemed simple, and a train ride from Brussels to Amsterdam was enough to get something working. I was informed that someone already attempted this approach earlier… This work was not shared with other Gluster developers, so the progress on it was also not clear :-/ After searching for proposed patches, we found that Prasanna did quite some work (patch v13) for this. He was expected to arrive after the meetup with the virtualization team was planned.

    Kevin did send me a detailed follow-up (in Dutch!) after he reviewed the current status of QEMU/gluster. There are five suggestions on his list, I will follow-up on that later (plus Prasanna and gluster-devel@).

    Snapshots of VM images can be done already, but they would benefit from reflink support. This most likely will require a REFLINK FOP in Gluster, and the appropriate extensions to FUSE and libgfapi. Something we might want to think about for after Gluster 4.0.

  • Finally, I met Csaba Henk in real life. He will be picking up adding support for Kerberos in the multitude of Gluster protocols. More on that will follow at some point.

DevConf.cz

Unfortunately, there was no Gluster swag or stickers at DevConf.cz, but this time there were Ceph items! It feels like the Ceph and Gluster community managers should work a little closer together so that we're evenly recognized at events. The impressions that I have heard, was like "Gluster is a project for community users, Ceph is what Red Hat promotes for storage solutions." I'm pretty sure that it is not the message we want to relay to others. The talks on Ceph and Gluster at the event(s) were more equally distributed, so maybe visitors did not notice it like I did.

During the Gluster Workshop (and most of the conference), there was very bad Internet connectivity. This made it very difficult for the participants to download the Gluster packages for their distribution. So instead of a very "do-it-yourself" workshop, it became more of a presentation and demonstration. From the few people that had taken the courage to open their laptops, only a handful of attendees managed to create a Gluster volume and try it out. The attendees of the workshop were quite knowledgeable, and did not hesitate to ask good questions.

After the workshop, there were more detailed questions from users and developers. Some about split-brain resolution and prevention, others about (again) the "backup-volfile-server" 'mount' option for QEMU. We definitely need to promote features like "policy based split-brain resolution," "arbiter volumes," and "sharded volumes" much more. Many users store VM images on Gluster and anything that helps improving the performance and stability gets a lot of interest.

Nir Soffer (working on oVirt/RHEV) wanted to discuss some more about improving their support for Gluster. They currently use FUSE mounts and should move to QEMU+libgfapi to improve performance and work around difficulties with their usage of FUSE filesystems. At least two things could use assistance from the Gluster team:

  • glusterfs-cli to be available for RHGS client systems
  • Sanlock improvements to use libgfapi instead of a filesystem

Speaking to Heinz Mauelshagen (LVM/dm developer) about different aspects of Gluster triggered a memory of something a FOSDEM visitor asked: Would it be possible to have a tiered Gluster volume with a RAM-disk as "hot" tier? This is not something we can do in Gluster now, but it seems that dm-cache can be configured like this. dm-cache just needs a block-device, and that can be created at boot. With some config-options it is possible to setup dm-cache as a write-through cache. This is definitely something I need to check out and relay back to the guy asking this question (he's in the interesting situation where they can fill up all the RAM slots in their server if they want).

Upstream testing the CentOS CI is available for many open source projects. Gluster will be using this soon for regular distaf test runs, and integration tests with other projects. NFS-Ganesha and Samba are natural candidates for that, so I encouraged Michael and Guenter to attend the CentOS CI talk by Brian Stinson.

Because the (partial) sysadmins for the Gluster infrastructure (Jenkins, Gerrit, others servers and services) have too little time to maintain everything, OSAS suggested to use the expertise of the CentOS team. Many of the CentOS core members are very experienced in maintaining many servers and services, the Gluster community could probably move much of the infrastructure to the CentOS project and benefit from their expertise. KB Singh sent an email with notes from a meeting about this topic to the gluster-infra list. It is up to the Gluster community to accept their assistance and enjoy a more stable infrastructure.

Wow, did you really read this up to here?! Thanks :)