O_NOATIME ?

[Paul Slootman]

On Wed 26 Oct 2016, devzero at web.de wrote:
> 
> since we are using rsync for backing up millions of files in a virtual environment, and most of the virtual machines run on SSD cached storage, i`d be curious how that negatively impacts lifetime of the SSD`s when we do rsync run every night for backup
> 
> my question:
> does rsync normal file comparison run to determine if anything has changed change atime of any files ?
> 
> for me it seems, stat/lstat calls of rsync do NOT modify atime, but i`m not sure under which conditions atime is changed. 

Most filesystems on modern linux systems should be mounted with the
relatime option.

The atime will then only be updated if either the mtime or ctime is
newer than the atime, or if the atime is older than a defined interval.

Note that simply using stat will not update the atime, as the *file*
itself has not been accessed, only its metadata.

There's also the nodiratime option that can be useful, as directories
are read to find what files exist in those directories; and it's
seldomly useful to maintain the atime of a directory.

You can also use noatime as a mount option, but then be sure that no
application uses the atimes of files; e.g. something like mutt use the
atime and mtime to determine whether there is a mail file with unread
mail.


Paul