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I am sorry that this came across this way. I did not intend to say bad things about GlusterFS but carve out where the technical differences are in the big pictu

by fh973 11y ago

I am sorry that this came across this way. I did not intend to say bad things about GlusterFS but carve out where the technical differences are in the big picture. Also I actually tried not to make any valuing statements. I am using the term split brain safety as technical term, ie. the P in CAP. My understanding is that GlusterFS does not have this in its system model and you and the documentation seem to support this: "This prevents most cases of "split brain" which result from conflicting writes to different bricks." Quobyte generally (and XtreemFS only for files) does quorum replication based on Paxos, where split brain is part of the system model. They are CP and hence data is not always available but is always consistent for reads if the quorum is there. Like Ceph. I am sorry that I missed the progress on placement. It seems like I need to catch up on what happened after the volume types.

notacoward 11y ago
"Split brain safety" is not a commonly used term, and even if that weren't the case I'd say it's not a term that should be thrown around lightly. Also, using Paxos or Raft doesn't guarantee split-brain safety, as aphyr has proven over and over again with Jepsen. So what we have is two systems that take different approaches to quorum and split brain and all that. It seems a bit disingenuous to throw stones at the older open-source project while ignoring the potential for the exact same problems in the newer proprietary one. FWIW, I do think the current Gluster approach to replication is not sufficiently resistant to split-brain in the all-important edge cases. That's why I've been working on a new approach, much more like Ceph and many other systems - though few of them use Paxos in the I/O path. That's wasteful. Other methods such as chain or splay replication are sufficient, with better performance, so they're more common.

by fh973 11y ago

notacoward 11y ago

"Split brain safety" is not a commonly used term, and even if that weren't the case I'd say it's not a term that should be thrown around lightly. Also, using Paxos or Raft doesn't guarantee split-brain safety, as aphyr has proven over and over again with Jepsen. So what we have is two systems that take different approaches to quorum and split brain and all that. It seems a bit disingenuous to throw stones at the older open-source project while ignoring the potential for the exact same problems in the newer proprietary one. FWIW, I do think the current Gluster approach to replication is not sufficiently resistant to split-brain in the all-important edge cases. That's why I've been working on a new approach, much more like Ceph and many other systems - though few of them use Paxos in the I/O path. That's wasteful. Other methods such as chain or splay replication are sufficient, with better performance, so they're more common.