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"ksmbd" is a new Linux kernel module which implements an SMB server. It's aimed at being low overhead, low footprint, performant fileserver covering many basic usecases, running on smaller devices with limited resources being the most apparent one: OpenWRT, the Linux distribution for embedded devices, adopted ksmbd already 18 months ago while ksmbd was still being developed.

ksmbd hit the public in November 2021 as part of the next Linux kernel version 5.15. It is not meant to replace the existing Samba fileserver "smbd", but rather be an extension and will integrate with Samba in the future. Samba's fileserver smbd is much broader in scope and supports various usecases and features that ksmbd does not:

• Running as a Active Directory domain member
• Scale-out clustering
• Optimize for specific filesystems like GlusterFS or Ceph via dedicated VFS modules
• Shadow Copy support

While being a mostly feature complete SMB3 server, lacking only some advanced features like Durable Handles, Directory Leases and Multi-Channel, ksmbd currently can only make use of local users and passwords which precludes use in corporate environments where typically Active Directory or similar identity sources are used.

ksmbd claims performance improvements on a wide range of benchmarks: the graphs on this page show a doubling of performance on some tests. There was also the notion that an in-kernel server is likely an easier place to support SMB Direct, which uses RDMA to transfer data between systems.

Clearly, those numbers are impressive, but at the same time recent improvements in Samba's IO performance put this into perspective: by leveraging the new “io_uring” Linux API Samba is able to provide roughly 10x the throughput compared to ksmbd.

Time will tell whether it's better to reside in kernel-space like ksmbd or in user-space like Samba in order to squeeze the last bit of performance out of the available hardware.

How mature is ksmbd? Given that its was primarily developed by a Samsung engineer, it is likely that it is being used in Samsung products today. However, the November release is a .0 release with all caveats that come with it. Some of the details, including various security issues that were found and fixed quite late in the game, are described in an article over at LWN.

All in all, ksmbd is an impressive work and in order to facilitate and encourage collaboration, the main ksmbd developer Namjae Jeon has been invited to join the international Samba team. ksmbd already adds interesting capabilities to the mix and the SerNet Samba team is looking forward to working with and on ksmbd!

This two-part article focuses on the strengths and advantages that make Samba unique. While part one took a look at some of the organizational, technical, and conceptual issues that are often discussed, this second part discusses technical milestones and improvements on the horizon, highlighting key Samba contributions still being worked on by the SerNet Samba Team members Volker Lendecke, Stefan Metzmacher and Ralph Böhme.

Robust and scalable – Multichannel Support for high performance
Sometimes Samba is criticised for "low concurrent connections / low concurrent opens". Because of the multiprocess model, which is more robust than a single-process multithreaded server model, Samba has higher RAM requirements than possibly other solutions. This is more relevant for the embedded SOHO router market than for enterprise storage solutions and to help the former the next Samba version will ship with a rewritten RPC-Server written by Volker Lendecke which results in a much smaller memory footprint.

SMB3 Multichannel support in Samba has been available since version 4.15 released in September 2021. The SerNet Samba team can provide stable backports to 4.12, 4.13 and 4.14 as we already have (and use) them in SAMBA+ 4.14 and custom packages.

Improving IO performance
Samba's IO performance is limited by the frequent data buffer copies done in the kernel for servicing Samba user space IO requests, resulting in high CPU usage and a CPU bound performance limit. This is an architectural limitation deeply rooted in the UNIX design. Two years ago a modern Linux API called “io_uring” has been added to Linux that allows user space applications like Samba to achieve zero-copy zero-syscall IO for the full IO path from disk to network. 

Recently, research on Samba performance improvements had been sponsored, and a Samba prototype was developed leveraging “io_uring”. We were able to improve IO performance drastically from 4 GBytes/s on a given hardware to 10 GB/s, the line speed of the 100 GBit/s adapter, with a significantly reduced CPU load of only 25%. Further testing using the loopback interface saw the throughput max out at up to 30 GB/s, the bottleneck being the clients used in testing (smbclient), not the server.

For more details see the discussion on the Samba list or the SDC 2021 presentation "Samba Multi-Channel/io_uring Status Update" from Stefan Metzmacher.

It would only take a few weeks of work to integrate the prototype into mainline Samba. Companies interested in this feature, please contact us to possibly join the list of companies sponsoring Samba development!

Samba supports Enterprise features
When it comes to clustering, you will get an "enterprise ready" SMB cluster from Samba. It supports scale-out active/active clustering and has been used for many years along with industry-leading clustered enterprise file systems like GPFS. Samba has plans to support “SMB Transparent Failover” and Ralph Böhme gave a talk at the SNIA SDC in 2018 on Persistent Handles in Samba. Again, companies interested in this feature, please contact us to possibly join the list of companies sponsoring Samba development!

ksmbd
Starting with Linux kernel 5.15, Linux will ship an in-kernel SMB server called “ksmbd”. ksmbd and Samba plan to work closely together in the future, and the main developer of ksmbd is as of recently also a member of the international Samba Team. Both projects will work hand in hand to combine ksmbd’s in-kernel SMB engine with Samba's user space daemons and tools. For a brief introduction, see the presentation from sambaXP 2019 (Slides) or the status update from sambaXP 2021(Slides).

Do you still have questions? Or would you like to talk to us about using Samba / SAMBA+? Then please feel free to contact us.

With immediate effect, Jule Anger takes over the release management in the international team of the open source software Samba.

The previous release manager Karolin Seeger joins Red Hat on October 1st 2021. She will hand over Samba team's release management to Jule Anger, who has been working as a developer in SerNet's Samba department for 2 years. At the same time Jule Anger officially becomes a member of the international Samba core team. The release management for Samba will thus continue to be sponsored by SerNet after the departure of Karolin Seeger.

Karolin's move also brings other changes: Ralph Böhme succeeds her as team leader of the Samba department at SerNet. He moved to SerNet and the Samba team in 2013 with the foreseeable end of Netatalk, the software he mainly supported for coupling Linux and macOS via AFP. Commenting on the arrival of Jule Anger, he says: "With Jule, we have a highly motivated colleague in our team and are very pleased that she will contribute to the Samba project on an international level with a breath of fresh air."

About SerNet: SerNet is the leading provider of services and products around the free software Samba and is active worldwide. With SAMBA+, SerNet offers its own professional Samba distribution.

The SerNet organization team has set the date for sambaXP 2022. The event is scheduled for May 31st to June 2nd. It will be the 21st international Samba user and developer conference – and hopefully a chance to reunite in person again after a long time.

As for now, it is planned that the conference will again take place on site at the Hotel FreizeitIn in Göttingen, Germany. Updates on the sambaXP 2022 as well as the call for papers will be published on the conference website https://sambaxp.org.

The whole team looks forward to see everyone in Göttingen again.