> Who "have to wait" ? Apps don't have to: they get the data from > cache and write to cache. Maybe the disk-write policy depends on the IO > scheduler as the read policy does, but this layer is completely isolated > from the applications.
Nope - not completely isolated. Applications that actually require on-disk consistency invoke things such as fsync(2). Every year or so there is a random blog post which notices that if you truly care about your data, you'd better do fsync(2), fdatasync(2) and/or rename(2) in the right places. If the os has done the write already, then this is pretty much a no-op, but if there are loads of stale write buffers your application can block until all of those have been written out and then performance craters. regards marc _______________________________________________ Dng mailing list [email protected] https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
