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Disk Journaling
Authored by: sebastienb on Apr 07, '03 03:04:58PM
"Disable Disk Journaling"

Ok, I've heard from both ends of the spectrum, some saying there's barely a difference, other saying it slows everything to a crawl, but never any real hard evidence. Does journaling really affect the system, and how so? Is it:

  • read/write speed?
  • CPU usage?
  • WHAT?!?!??!?!?!?
Does anyone have numbers, or *something* that quantifies any of these arguments?!?!?



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Disk Journaling
Authored by: aranor on Apr 07, '03 03:35:46PM

It will slow down file access (read/write) somewhat, but I have no data on how much. It probably really depends on the computer setup.



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Disk Journaling
Authored by: Bioinformatics on Apr 07, '03 05:55:41PM

I'm not an expert on this by any stretch of the imagination, but my impression is that journalled filesystems are shouldn't be that hard on system. They - in principle - should only tie up some RAM (for the tables they use), and soak up a little background CPU to write contents back to disk when CPU is available. There should be little effect on reading performance. How go the system is at balancing tasks might come in play, too. But none of this should be a bg hit on a well-configured system. There will be a little overhead - there is another system service running - but it shouldn't be dramatic.



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Disk Journaling
Authored by: DanFrakes on Apr 07, '03 07:03:13PM

According to Apple, the performance hit is significant. OS X Server (which offers journaling as a standard feature) has been tweaked to reduce this hit; however, OS X standard hasn't. I have a feeling that OS X standard will eventually offer journaling as a standard feature, and by that time OS X will have been tweaked to minimize this performance hit.

That being said, the truth is that journaling is really a server-level feature. It was developed for computers with very large volumes where (1) data integrity and (2) minimal downtime are of utmost importance. For the average user, you're better off keeping it disabled and simply backing up regularly, IMO. You'll get better performance, similar reliability, and more functionality (you'll be able to use fsck, Disk Warrior, and other disk utilities that can't be used on journaled systems without a bunch of caveats).



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Disk Journaling
Authored by: DaveD on Apr 08, '03 11:24:06AM

I'm sorry, but I must say that I disagree. I have used journaling file systems on BeOS, Linux (ext3, reiserfs, etc), and the journaling has in no way slowed down the system, or caused any sort of hit in system performance. While I am not saying that Apple's has issues, or that the slowdown is something that will be worked out as things mature, I do know that journaling should not cause a performance hit <when properly implemented>.



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Disk Journaling not a big deal
Authored by: SOX on Apr 07, '03 11:20:01PM

Reading what apples says about I think you can expect journalling to take a hit of
virtually zero on reads from disk
around 10% on writes to disk on average.

Note however writing to disk is not something you really do much of (compared to reading from disk). furthemore just because your writes are 10% slower does not mean your computer is 10% slower or tied up. Your computer can multi-task and while its waiting for disk seeks and such it may well be doing other things.

if 10% on write is keeping you up at nights (and personanlly disk error keep me up, not disk writes), then you can change the settings on journaling.

you do not have to journal your entire drive. you can selectively journal different chinks of the file system.
removing journalling from the swap partition, or /tmp makes complete sense and constitutes the majority of your disk activity when things seem to be getting slow anyhow. you could also create a filesystem directory that has journaling turned off where you can put all the large files you are writing that dont need the extra security provided by journalling (e.g. large photoshop files).



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Disk Journaling
Authored by: sgi_oh_too on Apr 07, '03 11:47:30PM

A while back, I wrote a research paper on journaling filesystems. Really, there can be a noticable amount of lag introduced depending on the implementation. SGI's XFS, Be's BeFS, IBM's JFS and softupdates in the BSD BFFS (not really the same as journaling) are by far the best implementations, and thus all result in 'almost' transparent operation in regard to speed. Hacked journaling add-ins like that of HFS et al ... are not usually good performers. If the rumor mill is correct, HFS may not be around much longer anyways. But, journaling is not just for servers, if you have a laptop, it can be invaluable in the situation of an empty battery. So, those of you that are with it, hop on the Darwin project and code us a new filesystem with metadata support and a good implementation of journaling! :)



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