TweetFollow Us on Twitter

Journaling Bits

Volume Number: 21 (2005)
Issue Number: 6
Column Tag: Programming

Journaling Bits

A Look At The OS X "Personal Diary"

by Brad Belyeu

Welcome

My typical work day is filled with interruptions. Phones constantly ringing; people asking questions, etc. Everyone wants a piece of my time. Interruptions are not only a major hit to productivity and effective time management; but when you're trying to replace a PowerBook logic board, it can mean bigger problems. They sometimes leave me wondering, "Where did I set my screwdriver?", or "Where does this screw go again?" Now imagine having a secretary that follows you around all day recording what you do. Whenever you finish a task, it is scratched off a list; and whenever you start a new task, it is added to a list. Anytime you had an interruption, you could simply ask your secretary what you were doing before the interruption. That would be amazing! This is what Apple's software engineer's were thinking when they introduced file system journaling.

Meet The Secretary

To understand why file system journaling is important, we need to understand file systems & take a look at OS X systems prior to journaling. File systems are like library cataloging systems. Library catalogs can tell you an exact name & location of any book in the library; just like file systems can tell you the exact name & location of a piece of data on a drive. Both systems regulate naming & location conventions for what they store. If a file system gets corrupted, it would be like trying to read a library catalog in a language you can't understand. Journaling was introduced into OS 10.2.2 Server edition and into the client in 10.3. In previous OS versions, when you have any of these failures, they leave your system volume in an unknown state because there is no record of where the disk was interrupted. The OS then had to do a data integrity check of the entire disk. Interruptions can also damage system files rendering the boot volume unusable. This is usually when you restart and are presented with a folder and the infamous flashing question mark because the computer can't find a disk to startup. But when journaling is enabled, the computer tracks file system operations and immediately logs them in a journal. When restarting after a failure, the operating system can use the journal to return the files system to its previous state. This eliminates the need to check the entire drive for inconsistencies. Instead, when the computer is restarted, it takes a look at its journal, reads to find out what it was doing, and picks up right where it left off. File system journaling is a major advancement in protecting the file system from power outages, hardware failures, or software crashes.

The Good

A system continuity failure interrupts the read & write processes of a hard drive. These interruptions create discrepancies between the file system (library catalog) and the actual location of the stored files (location of books in library). In a journaled file system the OS has a record of disk activity, preventing the disk from becoming unusable (most of the time) which also prevents repairs that cost both time & money. It also cuts down on the time it takes to restart the computer after one of these failures because the entire disk doesn't have to be checked for inconsistencies block-by-block. Although a multi-gigabyte hard drive only takes several minutes to check, the original idea in introducing file system journaling was to minimize down-time for servers because a multi-terabyte disk could take hours to check. A journaled file system takes just a few seconds to return to operating condition no matter what the size of the drive is.

File system journaling was developed by Apple to be an extension to the current file system. This is good news because it lets you enable/disable journaling without reformatting the disk! The Mac OS Extended volume format (HFS+) can change between journaled and non-journaled without any data loss. The advantages of this will become clear later in the article as we discuss reasons you may not want to use file system journaling.

Because the journal works at the system level, it is invisible to the applications on the drive. Other than some disk utilities, all applications and network setups are compatible with journaling. Most 3rd party disk utilities will also work with journaling. Just in case you were wondering, finished actions are removed from the journal so the journal file doesn't become too large. Just like that the secretary crosses completed tasks off your list and throws them in the trash.

Journaled file systems are backward compatible with the regular HFS+ file systems. Meaning that computers using an older Mac OS can have full access to journaled volumes. This is great news for external hard drive users with multiple computers. That way you can use journaling on your hard drive and all your Macs can use the drive whether they are running OS 10.3 or an earlier version.

The Not So Good

Journaling doesn't come without its cost, which happens to be performance. But fortunately, the performance hit only comes when the system is writing to the disk and not when it is reading from the disk. I've never been able to actually tell the difference in speed on drives running journaled verses non-journaled drives. Supposedly, if you have a client version of the OS, the performance hit can be up to 20%, but the server version of the OS comes with a buffered version of journaling. If you have enough RAM, the server version is only supposed to take a 2-3% hit on hard drive performance.

Here's my general opinion on two occasions when you shouldn't use journaling. If you have a drive that is primarily set up to be read-only access, you don't need journaling. For example, if you have a hard drive that you keep your applications on (or just the OS), but not your actual documents or working files on, then you probably don't need file system journaling. This is because you are just pulling data off the drive 99% of the time and are rarely saving data back to the drive. If your system fails, your drive probably wasn't in the middle of writing data. Or if you have a file server disk that is always under heavy speed demands AND you back it up on at least a daily basis, I would consider disabling file system journaling. This might be the case if you are storing large data files containing audio or video that are accessed frequently.

Although file system journaling will help you save data that has already been journaled to your drive; you may still lose data in the event of a failure that is in the buffer before it is written to the drive. So file system journaling definitely needs to be complimented by a battery backup system.

The last drawback to consider is the failure of some 3rd party disk utilities to work with file system journaling. Make sure you check compatibility on a manufacturer's website before using a 3rd party utility on a journaled file system. Many of the vendors released updates specifically for their product to work with a journaled file system. I've heard nightmares of people losing all their data by running an incompatible disk utility with a journaled file system.

File system journaling has its limitations and is not a fix-all answer to your data problems. According to Apple, file system journaling is one of several measures you should take to avoid data loss. File system journaling should be coupled with RAID (redundant array of indexed disks) storage, a continuous backup strategy, and an uninterrupted power source (UPS) for maximum protection of you digital assets.

Enabling/Disabling

You can enable or disable file system journaling using Disk Utility (located in the Applications/Utilities folder). Select a volume in Disk Utility (figure 1).


Figure 1.

If you want to enable journaling, you can simply click 'Enable Journaling' from the pane. This will enable journaling without erasing data on the disk. If you'd like to disable journaling, you can select the volume and then click File-Disable Journaling from the menu bar.

You can also enable or disable file system journaling using the command line version of Disk Utility, diskutil. To have sufficient privileges you'll have to use sudo (super user do) with diskutil. To enable file system journaling on the root directory type:

sudo diskutil enableJournal /

and then type in your administrator password. If you'd like to disable file system journaling on the root directory use:

sudo diskutil disableJournal /

followed by your administrator password. To enable or disable on volumes other than the startup disk replace / with /Volumes/(VolumeName).

Repairing Journaled Drives

To repair an ailing journaled drive you can once again use Disk Utility. The trick is that you can't repair the disk you booted from; so if you want to repair your startup volume with Disk Utility, you have to startup to a CD or another drive. Once you have Disk Utility open, select the drive that you want to repair and then click 'Repair Disk'. If you don't have another drive you can startup from you'll be better off using a 3rd party utility or the command line.

If you don't want to spend the money on a 3rd party disk utility, try using the command line utility fsck_hfs. To force fsck_hfs to check a journaled volume you need to use the argument -f. Also, if you just want to verify status of the drive, use the -n flag; but if you want to repair the drive, use the -y flag.

There are a number of excellent 3rd party disk utilities. My favorite are DiskWarrior X & TechTool Pro. There are also a number of shareware & freeware applications to be found just by searching versiontracker.com or macupdate.com.

Wrapping up Journaling

Using file system journaling is a great idea for most users. There are the occasions to disable it, but for the most part it makes our lives easier. That is where the analogy leaves the library catalog. File system journaling is done automatically, but looking up a book in a library can sometimes be challenging. I'm just glad file system journaling keeps track of everything without my lifting a finger. But remember, file system journaling does not excuse you from needing a regular system backup!


Brad Belyeu is the President of ABConsulting based out of Oklahoma City, OK. He is an Apple Certified Technician and a certified member of the Apple Consultant Network. Most importantly, he is happily married.

 
AAPL
$100.57
Apple Inc.
+0.04
MSFT
$44.95
Microsoft Corpora
-0.38
GOOG
$584.49
Google Inc.
-2.37

MacTech Search:
Community Search:

Software Updates via MacUpdate

Picasa 3.9.138 - Organize, edit, and sha...
Picasa and Picasa Web Albums allows you to organize, edit, and upload your photos to the Web from your computer in quick, simple steps. Arrange your photos into folders and albums and erase their... Read more
Tidy Up 3.0.15.0 - Find duplicate files...
Tidy Up is a complete duplicate finder and disk-tidiness utility. With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator, extension, time... Read more
Parallels Desktop 10.0 - Run Windows app...
Parallels Desktop is simply the world's bestselling, top-rated, and most trusted solution for running Windows applications on your Mac. With Parallels Desktop for Mac, you can seamlessly run both... Read more
Apple Final Cut Pro X 10.1.3 - Professio...
Apple Final Cut Pro X is a professional video editing solution.Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Apple Compressor 4.1.3 - Adds power and...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Powerful... Read more
Chromium 36.0.1985.143 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. FreeSMUG-Free OpenSource Mac User Group build is... Read more
Macgo Blu-ray Player 2.10.6.1691 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple Motion 5.1.2 - Create and customiz...
Apple Motion is designed for video editors, Motion 5 lets you customize Final Cut Pro titles, transitions, and effects. Or create your own dazzling animations in 2D or 3D space, with real-time... Read more
A Better Finder Rename 9.39 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
PopChar X 6.6 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more

Latest Forum Discussions

See All

Cubic Castles Review
Cubic Castles Review By Rob Thomas on August 20th, 2014 Our Rating: :: CASTLE CRAFTINGiPad Only App - Designed for the iPad Some ridiculously frustrating camera issues aside, Cubic Castles is a pretty neat, voxel-based crafting... | Read more »
Space Colors – Tips, Tricks, Strategies,...
Hello Cadets: Want to know what we thought about this hectic space combat/roguelike? Check out our Space Colors review! Space Colors is a cool shooter/roguelike from Team Chaos. You travel from planet to planet across a huge galaxy and complete a... | Read more »
Tap Sports Baseball – Tips, Tricks, and...
Tap Sports Baseball is a pretty simple game to learn, but that doesn’t mean it’s an easy game to master, by any means. To start your batting career off well, we thought we’d give you the heads up on some handy tips and tricks. Hey Batter-Batter:... | Read more »
Tap Sports Baseball Review
Tap Sports Baseball Review By Jennifer Allen on August 20th, 2014 Our Rating: :: LET'S PLAY BALLUniversal App - Designed for iPhone and iPad Tap Sports Baseball is briefly fun but lacks some important features.   | Read more »
Earn to Die 2 Set to Drive in to the App...
Earn to Die 2 Set to Drive in to the App Store Later This Year Posted by Ellis Spice on August 20th, 2014 [ permalink ] Not Doppler has announced that Earn to Die 2, a sequel to their successful game | Read more »
Frontier Heroes Review
Frontier Heroes Review By Andrew Fisher on August 20th, 2014 Our Rating: :: BLAZES NO TRAILSUniversal App - Designed for iPhone and iPad Despite awesome visuals and great music, Frontier Heroes just doesn’t quite deliver enough fun... | Read more »
Echo Prime is Now on Sale for $0.99
Echo Prime is Now on Sale for $0.99 Posted by Jessica Fisher on August 20th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Star Realms Review
Star Realms Review By Andrew Fisher on August 20th, 2014 Our Rating: :: A STAR IS BORNUniversal App - Designed for iPhone and iPad Star Realms is an excellent adaptation of an outstanding deck-builder. With great visuals and an... | Read more »
This. Is. SPRINGFIELD! War comes to The...
This. Is. SPRINGFIELD! | Read more »
One Tap RPG Review
One Tap RPG Review By Campbell Bird on August 20th, 2014 Our Rating: :: DUNGEON SLIDERUniversal App - Designed for iPhone and iPad This casual arcade game introduces some very light rpg elements into its fantasy-themed pachinko... | Read more »

Price Scanner via MacPrices.net

Apple now offering certified refurbished 2014...
 The Apple Store is now offering Apple Certified Refurbished 2014 MacBook Airs for up to $180 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Best Buy’s College Student Deals: $100 off Ma...
Take an additional $100 off all MacBooks and iMacs, $50 off iPad Airs and iPad minis, at Best Buy Online with their College Students Deals Savings, valid through September 6th. Anyone with a valid .... Read more
MacBook Airs on sale for $100 off MSRP, free...
B&H Photo has three 2014 MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for Laptops... Read more
Razer Taipan Mouse For Gamers And Non-Gamers...
If you’re a serious gamer on either Mac or Windows PCs, a serious gaming mouse is a necessity for first-tier performance. However, even if like me you’re not much of a gamer, there’s still a strong... Read more
15-inch 2.2GHz MacBook Pro on sale for $1899,...
Adorama has the new 15″ 2.2GHz Retina MacBook Pro on sale for $1899 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this... Read more
Mid-Size Tablet Shootout Posted: iPad mini wi...
I ‘m curious about how many iPads Apple is actually selling these days. It’s been widely rumored and anticipated that new models with A8 SoCs, 2 GB of RAM, 8 megapixel cameras, and fingerprint... Read more
The 15 Biggest iPad Air Problems And How To A...
What’s this? Fifteen “biggest” problems with the iPad Air? Does that mean there are a lot of smaller problems as well? Say it isn’t so! My old iPad 2 has manifested no hardware problems in three... Read more
TYLT Syncable-Duo, 2-in-1 USB Cable With Appl...
TYLT has introduced the Syncable-Duo, a universal cable solution for charging and syncing data to smartphones and tablets. The Syncable-Duo eliminates the need for multiple cables by incorporating... Read more
Save up to $140 off MSRP with Apple refurbish...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
2.5GHz Mac mini on sale for $549, save $50
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant - Apple (United...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** Being a Business Manager at an Apple Store means you're the catalyst for businesses to discover and leverage the power, ease, and flexibility of Apple Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.