My only personal interest in O_DIRECT is for KVM qemu virtualization. It sounds like I will probably need to set direct=disabled. Alternatively, if I could get all the writes to be 4K-aligned (e.g. by making all the virtual disks 4Kn?), then ZFS's O_DIRECT would work.
The rest are some questions for here or the call tomorrow, if you think they're worthwhile: On 3/30/20 5:29 PM, Matthew Ahrens via openzfs-developer wrote: > It is also a request to optimize write throughput, even if > this causes in a large increase in latency of individual write requests. This was surprising to me. Can you comment on this more? Is this true even in scenarios like databases? (I honestly don't know. This is above my level of expertise.) > For write() system calls, additional performance may be > achieved by setting checksum=off and not using compression, > encryption, RAIDZ, or mirroring. Is there a likely use case for this scenario? Databases always come up in O_DIRECT discussions, but having to have no redundancy to get the most performance is a serious limitation. (Note: I have no idea how expensive the one copy is.) > “Always”: acts as though O_DIRECT was always specified What is the use case for this? -- Richard ------------------------------------------ openzfs: openzfs-developer Permalink: https://openzfs.topicbox.com/groups/developer/T950b02acdf392290-M3a4efe289df16d2eec23d18f Delivery options: https://openzfs.topicbox.com/groups/developer/subscription
