As usual, Theodore Ts'o the linux filesystem guru makes interesting
reading...
Whilst wading through his blog [1] I came across his suggestion of "chattr +A".
This got me intrigued and I did a bit of reading and my conclusions
are this..
* Every time you access a file for whatever reason, POSIX writes an
"atime" timestamp. 99.9999% of the time you don't care. (It's the
"last modified" "mtime" timestamp you do care about!)
* Mounting a filesystem with "noatime" is a big win over mounting
with "relatime" or worse with "atime".
* You can use
chattr +A /some/path/
to mark a subdirectory as NoAtime, and all files and subdirectories
of /some/path inherit that attribute.
* You should mark things like /home with
chattr +T /home
A directory with the 'T' attribute will be deemed to be the top of
directory hierarchies for the purposes of the Orlov block allocator.
This is a hint to the block allocator used by ext3 and ext4 that the
subdirectories under this directory are not related, and thus should be
spread apart for allocation purposes. For example it is a very good
idea to set the 'T' attribute on the /home directory, so that
/home/john and /home/mary are placed into separate block groups. For
directories where this attribute is not set, the Orlov block allocator
will try to group subdirectories closer together where possible.
This attribute is not inherited by subdirs.
I install our cross compiler tool chain in /opt and I have taken to
marking it as...
chattr +AT /opt
I have also added a "chattr +A" to the script that checks out our
code.
Comments / suggestions welcome.
John Carter Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : [email protected]
New Zealand
[1] http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/
