First of all, use ls -ls --block-size=1 or du -B 1 to read physical file size. Physical file size traditionally means how much physical disk space this file has taken. However this is not true in ZFS. I performed some experiments and it is not affected by vdev type and level of raidZ but apparently affected by compression and other fs metadata like extended attributes.
这里只指出一个重点:SMTP 将电邮区分为 Envelope 和 Data 两部分。通常我们在邮件客户端里见到的所有东西都属于 DATA ,包括 From:和 To:字段(也就是我们通常见到的收件人发件人)。然而所谓 Envelope 也有 MAIL FROM 和 RECP TO 数据,并且这二者和 DATA 里的 FROM/TO 一般并不一致!下文将详细展开。