The vfs.write_behind sysctl variable defaults to 1 (on).
This tells the file system to issue media writes as full
clusters are collected, which typically occurs when
writing large sequential files. The idea is to avoid
saturating the buffer cache with dirty buffers when it
would not benefit I/O performance. However, this may
stall processes and under certain circumstances you may
wish to turn it off.
Looking through the documentation, I can't find an explaination
of what a cluster is. Multiple blocks?
How would this stall processes? Seems backwards. If you don't
have write-behind, a process would block until the data gets
written to the media.