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Related to the “Which volume types generally allow Read Write Many (RWM) access mode?” question in K8s deep dive course

The answer to this question in the quiz is "File-based volumes" but I couldn’t really understand why and the link provided in the answer didn’t seem to add more clarity. https://kubernetes.io/docs/concepts/storage/persistent-volumes/#access-modes.

Any ideas why this might be the case?

2 Answers

In thinking how the various forms of AWS storage work, I believe it comes down to how many resources can mount (or act upon) that storage resource at the same time. For example, an SSD or block storage device can only be mounted by a single EC2 instance so it would be ReadWriteOnce (only one device can read/write to it). A read-replica SQL db might be a ROX as many devices can connect and read data from it, but they cannot write to it. File-based volumes (or file shares like EFS & FSX) have the ability for numerous (Many) resources to connect to them and read/write data to that drive at the same time. This may not be 100% accurate, but that was the logic I worked through on answering that question. Hope that helps, someone please correct me if I mispoke on any of that.

It’s down to the differences between mounting a block storage and file system storage.

It’s no different in the world of virtual machines, for example, you could mount a single HDD (or LUN from a SAN) to a single virtual machine and then create a file system on top of that block storage, you couldn’t mount this HDD to multiple virtual machines at the same time. On the other hand a file storage mount, say a NFS/SAMBA share, could be mounted to multiple virtual machines at the same time.

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