> b. other FSes which do not have CoW support. ext4 is already being > used for "atomic writes" in the field We also need raw block device access to work within the constraints required by the hardware. >> probably want to do it for optimal performance, but requiring it >> feeels rather limited. The application developers we are working with generally prefer an error when things are not aligned properly. Predictable performance is key. Removing the performance variability of doing double writes is the reason for supporting atomics in the first place. I think there is value in providing a more generic (file-centric) atomic user API. And I think the I/O stack plumbing we provide would be useful in supporting such an endeavor. But I am not convinced that atomic operations in general should be limited to the couple of filesystems that can do CoW. -- Martin K. Petersen Oracle Linux Engineering
