I was recently asked which trade-offs LINBIT’s solution chose under the CAP theorem. The CAP theorem says that a distributed system can provide only two out of three properties: Consistency, Availability, and Partition tolerance.
As you can read in the linked article, all practical systems must tolerate partitioning, which leaves us with the choice of whether the software provides consistency (and partitioning Tolerance) or availability (and partitioning Tolerance).
By default, LINSTOR generates resources with quorum enabled. In the words of the CAP theorem, these resources are CP. They do not provide availability because DRBD denies access to the data if a partition loses quorum,
If you turn off quorum on a DRBD resource the resulting system is AP in CAP terminology. Data is always accessible for the price of perhaps granting access to a replica not in sync with other nodes. That might even lead to the infamous split-brain. So, you better not disable quorum.
AC is academic only. It would mean you provide an unfailable network and undestroyable nodes and you expect availability and consistency. Purely theoretical.
In conclusion, the answer is LINBIT SDS, and LINBIT HA can do AP and CP in the CAP theorem wording; you decide with your configuration.
After this excursion into the world of computer science theory, let’s turn our attention to the update to the LINBIT signing keys. The original package signing key is showing its age, and we have to start with a new one that follows the recent developments in cryptography.
Moving on to new LINBIT content, I have several YouTube videos to share this week. The videos are products of our Q3 Community Meeting last month, as we decided to release each segment individually.
We began the meeting with my segment, after a ‘mysterious’ and ‘exciting’ introduction, which was ‘LINBIT Introduces the Open Source GUI for Managing LINSTOR for SDS, HA, & DR.’ I took the viewers through a demonstration of the GUI, and the video description includes a link from which you can download the GUI.
The segment titled ‘EDR, XDR, Data Replication Network Traffic, and Virtualization and Hypervisor Management Software’ is something of a deep dive into some results from LINBIT troubleshooting for a customer who was having issues with the LINBIT SDS integration for Apache CloudStack.
‘Introducing the LINBIT Community Forums’ provides an overview of our relatively new forum, explaining what users can expect when they decide to use it, either as a poster searching for a solution or a contributor.
Last but not least, ‘Rewriting DRBD Proxy in Rust For Long Distance Data Replication’ overviews the efforts to modernize and improve the software for better maintainability.
We have also updated the blog, ‘Managing DRBD By Using systemd Units’, was created by LINBIT CTO Lars Ellenberg and LINBIT Solutions Architect Yusuf Yıldız. It outlines how to safely manage DRBD resources with systemd as an alternative to a CRM. As the article says, this introduction should cover most use cases, but we recommend reaching out if there’s anything else you’d like to know. You can even try our forum.
Regarding new software updates, we released LINSTOR GUI v1.8.4. Visit the link to see the changelog and access the update.
