I am copying 36T of data from one drive (hardware RAID 6 array) to another on a machine with some large jbod's. This machine is a server with two E5-2667v2 processors in it (so that you may ponder its vintage), running CentOS 6.4, kernel 2.6.32-358.23.2.el6.x86_64, rsync  version 3.0.6  protocol version 30. I noticed that the rsync I ran: rsync -av source /path/to/dest starts 3 processes, two of which do the heavy lifting. There's a reader that stuffs the data out of a socket to a writer that receives it, then dumps it into the current file.The reader rsync writes its data on the pipe in operations of alternate 4092 and 4 bytes. Why? Isn't that inefficient?I'm getting 130 MB/s on my copy and I'd like to speed it up. The jbod's are on separate PCIe RAID cards which support 6 Gbps SAS.Here is a bit of strace output of the reader; as I said it's writing its data out to a socket (File descriptor 4):write(4, \0_\220l\0\0\0\0\0a\220l\0\0\0\0..., 4092) = 4092write(4, \374\17\0\7, 4)              = 4write(4, \0\0\0\0\0\247\223l\0\0\0\0\0\25..., 4092) = 4092write(4, \374\17\0\7, 4)              = 4
Why does the rsync reader perform two writes per 4k of data?
linux;files;rsync