不更新文件系统上 inode 访问记录，可以提升性能。
noatime 选项阻止了读文件时的写操作。大部分应用程序都能很好工作。只有少数程序如 Mutt 需要这些信息。Mutt 的用户应该使用
relatime 是比较好的折衷，Mutt 等程序还能工作，但是仍然能够通过减少访问时间更新提升系统性能。
Do not update inode access times on this filesystem (e.g., for faster access on the news spool to speed up news servers).
不更新文件系统上的目录 inode 访问记录，可以提升性能。
实时更新 inode access 记录。只有在记录中的访问时间早于当前访问才会被更新。（与 noatime 相似，但不会打断如 mutt 或其它程序探测文件在上次访问后是否被修改的进程。），可以提升性能。
Update inode access times relative to modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time. (Similar to noatime, but doesn’t break mutt or other applications that need to know if a file has been read since the last time it was modified.)
Since Linux 2.6.30, the kernel defaults to the behavior provided by this option (unless noatime was specified), and the strictatime option is required to obtain traditional semantics. In addition, since Linux 2.6.30, the file’s last access time is always updated if it is more than 1 day old.
This disables the use of write barriers in the jbd code. This also requires an IO stack which can support barriers, and if jbd gets an error on a barrier write, it will disable again with a warning. Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance penalty. If your disks are battery-backed in one way or another, disabling barriers may safely improve performance. The mount options “barrier” and “nobarrier” can also be used to enable or disable barriers, for consistency with other ext4 mount options.
All data are committed into the journal prior to being written into the main file system.
Data ordering is not preserved, data may be written into the main file system after its metadata has been committed to the journal.
Use default options: rw, suid, dev, exec, auto, nouser, and async.
(*) Defer block allocation until just before ext4 writes out the block(s) in question. This allows ext4 to better allocation decisions more efficiently.
Disable delayed allocation. Blocks are allocated when the data is copied from userspace to the page cache, either via the write(2) system call or when an mmap’ed page which was previously unallocated is written for the first time.
Controls whether ext4 should issue discard/TRIM commands to the underlying block device when blocks are freed. This is useful for SSD devices and sparse/thinly-provisioned LUNs, but it is off by default until sufficient testing has been done.
IMPORTANT: Do not discard blocks in filesystem usage.
Be sure to turn off the discard option when making your Linux filesystem. You want to allow the SSD manage
blocks and its activity between the NVM (non-volatile memory) and host with more advanced and consistent
approaches in the SSD Controller.
• ext4 – the default extended option is not to discard blocks at filesystem make time, retain this, and do not
add the “discard” extended option as some information will tell you to do.
• xfs – with mkfs.xfs, add the –K option so that you do not discard blocks.
If you are going to use a software RAID, it is recommended to use a chunk size of 128k as starting point, depending
on the workload you are going to run. You must always test your workload.