Thanks for your suggestions. Unfortunately, now I'm not confident in these results, because today this behavior is not happening, even with the same zpool on the same system. Now it's writing at a steady rate to disks the whole time, instead of starting out very high (3GBps to memory) and then dropping to zero at the end. So essentially the fsync doesn't have to sync anything at the end. Is there some way to control this behavior? I'm not sure if it's fio or the filesystem, but why does it write at disk speed today, while it wrote at memory speed before?
