Hello John,
On Friday 18 August 2006 17:27, John Goerzen wrote:
> Hi,
>
> In reading about the keepatime option and in reading the source, I think
> there is a much better way to accomplish this, on Linux at least.
>
> On Linux, since 2.6.8, there is an O_NOATIME flag that can be passed to
> open(2). The open(2) manpage states:
>
> O_NOATIME
> (Since Linux 2.6.8) Do not update the file last access
time
> (st_atime in the inode) when the file is read(2). This flag
is
> intended for use by indexing or backup programs, where its
use
> can significantly reduce the amount of disk activity. This
flag
> may not be effective on all filesystems. One example is
NFS,
> where the server maintains the access time.
>
> I think it would be desirable to support this mechanism over the
> keepatime mechanism, which calls utime() to modify the atime and has the
> associated problems involving modifying the ctime.
>
> This would also *speed up* rather than slow down backups, since the
> filesystem would not have to write updated metadata after each file was
> accessed.
I am pleased to say that this option is implemented in version 1.39.x (and in
the current 1.39 beta version). Here are my current ReleaseNotes on this
item:
- Apply a patch submitted by cesarb in bug #606 to implement O_NOATIME
support.
O_NOATIME is a open() flag which makes it possible to read a file without
updating the inode atime (and also without the inode ctime update which
happens if you try to set the atime back to its previous value). It also
prevents a race condition when two programs are reading the same file, but
only one does not want to change the atime. It's most useful for backup
programs and file integrity checkers (and bacula can fit on both
categories).
You enable it in the Bacula FileSet Options resource by setting:
noatime = yes
The effect of this option is similar to the keepatime option except
it is more efficient and avoids modifying ctime.
Best regards,
Kern
>
> -- John
>
>
>
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