Mac Forum / General / General / October 2005

Never had any problems with it whatsoever on any of our Macs at work or mine
at home.  With Jaguar or Panther.  So don't have any advice other than it
was a no-brainer.

Greg

Well, I could tell you the advice I get from the people here who are
too inconsiderate to offer direct advice, but who feel compelled to
beat down guys like us.  They would say this question has been answered
innumerable times, and that you should waste hours of your time
searching Google for answers, instead of bothering them.

...but I could not do a dirty trick like that to you.<g>

Apple (and others) - in their infinite wisdom, try to make everything
possible automatic.

Er,  _except_  the things that  _I_  prefer that they make automatic.

But it is their OS, so they can do anything they darn well please, and
don't have to listen to their customers if they don't want to.

This is going to be a long explanation, so sit down and get comfortable.

I am going to give you the long version, so you fully understand it.

That is the prime reason for journaling, to enable you to protect the
_file_  system against being corrupted, when you have a power
interruption.   Notice I said protects the file system, not the file
being written to disk at the time of the power interruption.

This indeed would make it easier to get running again after a power
interruption.  (on a desktop Mac)

Being powerbooks run off battery power, it is very unlikely that a
power failure would affect them, even if they were plugged into the AC
outlet, because their battery would prevent them from losing power.

Background Info', Necessary to Fully Understand Journaling -
********************************************
A file system of some sort can be considered to be a necessary  _part_
of the operating system, but just a tiny small part, generally just a
few megabytes in size.

BEFORE you install the OS, you install an approved default file system,
usually a HFS+ file system.   This is normally done by you before OS X
is even installed - - - when you "prepare" your hard drive by erasing
it, partitioning it, or whatever you do to get the drive icon to appear
on the screen of your computer.

If you  _don't_  install an "approved" file system of some kind on your
hard drive, the drive's icon might not even appear on your screen.  
You will get an error message something like this:

"An unrecognizable drive is attached to this computer, do you want me
to initialize it?"

Sometimes that message will appear if a hard drive was used on a
Window's computer.   There  _is_  a file system, a Window's file
system, which the Mac simply might not "recognize".

...or, some dirty guy like me might have erased all traces of any sort
of file system whatever, from the drive.
(its a lot of work, but it  _can_  be done)

Whatever the reason, your Jaguar CD will refuse to install OS X until
you let it install an "approved" file system first.

It will give you your choice of HFS+ (extended) - - - or UFS.

UFS is only used by Unix geeks, so the Jaguar install CD will probably
gently nudge you to use the regular HFS+ "extended" default variety of
file system.

Okay, the Jaguar CD installs a default file system, then it proceeds to
install the Jaguar OS itself.

The invisible file system files get updated to reflect where each file
was placed on the disk, what kind of file it was, what kind of app'
will be used to open the file, when each file was written to disk, and
a lot of other details about the files.
*********************************************
End of Background Info' -

Okay, back to Journaling.

Let's look at one other reason for journaling.

Files in OS X are constantly changing in size, some file segments are
automatically deleted, some files grow in size, some files may be
automatically compressed, other files may be automatically defragged,
which means the segments of those defragged files get moved to other
locations on the disk.

Time is consumed as all of these many changes are written to the file
system area of the disk, in order to keep track of where files are
located on the disk.

That "file system housekeeping" time is taken away from any disk chores
that  _you_  want to do, like downloading a file from the Internet.

A journaling system allows you to postpone some of this disk writing to
the file system area, keeping track of all the file system changes in
fast RAM instead, then later, writing all the changes to disk at once.

This saves the time that would ordinarily be lost by many slow disk
constantly interrupting its "legitimate" work in order to update the
file system area of the disk.

All that said, journaling itself slows down some operations about 5%
according to some reports.   I have read that some users prefer to shut
off journaling when their Macs are doing CPU intensive tasks, like
displaying full screen movies, for example.

Keep in mind that the  MAIN  reason for journaling is to prevent
_some_  of the damage that would be done in case of a power
interruption, or the rare crash of the OS itself.

FWIW, here I have operated both ways, sometimes leaving journaling on
for months at a time, sometimes leaving it off for months at a time.

Generally, when I think of it, I guess I prefer to leave it off.

However, if I were doing a lot of disk intensive tasks, my preference
then would shift to keeping it on, to possibly speed up those disk
tasks a tiny bit.

My rule of thumb, leave it on for disk intensive tasks, leave it off
for CPU intensive tasks.

Confusing, isn't it.<g>

I don't really worry about power interruptions here, even though they
occur often due to my rural location and unreliable power.

I run powerbooks exclusively, and I also have them running from
un-interruptible power supplies - - - so over the years no power
interruption has zapped my Macs.

If I ran desktop Macs, I  _might_  engage journaling.

Then again, perhaps not.

Everyone has to make up their own mind.   Most Mac users just leave
journaling on.   Journaling with Tiger is turned on by default.

Mark-

A few more things about journaling I saved for this follow-up post.

Bob Harris is our resident expert on journaling, wish he would pop in
to supplement this thread with his expertise.

Apparently, some of the journal information is also kept on disk if I
understood Bob Harris correctly.  This is important in some situations.

For example, if you are running a big honking Mac server, with a
hundred times more files than we run in our hobby Macs - - -

Imagine such a server has a power outage.   Well, ordinarily, when you
fire it back up again, fsck runs automatically to try to repair the
file system that was messed up by the power outage.

WITHOUT  journaling, fsck has to check  _each_   _one_   of potentially
millions of files, which  _could_  take as long as 30 minutes.

WITH  journaling, a lot of this info is on disk, so fsck would only
take perhaps one minute to run its file system repairs, because fsck
could "play back" a lot of the journal info' and therefore fsck would
be saved from needing to check  _all_   the files on disk.

This saving of time is important if you are trying to get a huge
critical server back on the air.

Not so important on our hobby Macs.

Mark-