Linked by Rahul on Sat 18th Oct 2008 11:29 UTC
Linux While Ext4 was originally merged in 2.6.19, it was marked as a development filesystem. It has been a long time coming but as planned, Ext4dev has been renamed to Ext4 in 2.6.28 to indicate its level of maturity and paving the way for production level deployments. Ext4 filesystem developer Ted Tso also endorsed Btrfs as a multi-vendor, next generation filesystem and along with the interest from Andrew Morton, Btrfs is planned to be merged before 2.6.29 is released. It will follow a similar development process to Ext4 and be initially marked as development only.
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Defragmentation
by adkilla on Sat 18th Oct 2008 16:22 UTC
adkilla
Member since:
2005-07-07

Is ext4 less prone to performance degradation on filesystems with less space for defragmentation?

I've read that it improves this situation somewhat but no specifics thus far.

Reply Score: 1

RE: Defragmentation
by NxStY on Sat 18th Oct 2008 16:41 in reply to "Defragmentation"
NxStY Member since:
2005-11-12

Ext4 has some features to reduce fragmentation, delayed allocation for example. There will also eventually be an online defragmenter.

Reply Parent Score: 7

RE[2]: Defragmentation
by adkilla on Sat 18th Oct 2008 17:01 in reply to "RE: Defragmentation"
adkilla Member since:
2005-07-07

Doesn't ext3 already have an online defragmenter? I recall that the major drawback of it that it needs a significant amount of freespace to be effective.

From wikipedia:
http://en.wikipedia.org/wiki/Ext4

"Ext4 will eventually also have an online defragmenter. Even with the various techniques used to avoid it, a long lived file system does tend to become fragmented over time. Ext4 will have a tool which can defragment individual files or entire file systems."

Reply Parent Score: 1

RE: Defragmentation
by segedunum on Sat 18th Oct 2008 17:00 in reply to "Defragmentation"
segedunum Member since:
2005-07-06

No too sure what you mean, as ext3 had no official defragmentation tool (I'm assuming you're comparing ext4 to something). It kept fragmentation to a minimum by allocating blocks that were closest to a file, but inevitably, this compromised other things and you still got fragmentation over time. This was alright in fairly static partitions such as /, /usr etc. but killed partitions with lots of file activity over time. ext4 has online defragmentation and also support for extents, which filesystems like XFS have provided for some time.

You can't break the laws of physics though. If you are going to defragment then you have to have enough free space to move all your files around, and if you don't then parts of your filesystem will simply stay fragmented with all the performance issues that entails.

However, defragmentation is merely a necessary evil with today's storage technology and you can only do so much. If SSDs kick on over the next few years and we get the same random read and write access no matter where in a storage device a file block is allocated, then fragmentation issues will start to disappear. There are actually many ways you can defragment and order data with today's mechanical disks with respect to performance. It really depends on the type of data and usage, and that's what is so difficult. Any person who tells you that a modern filesystem can solve all that is well wide of the mark.

Reply Parent Score: 1

RE[2]: Defragmentation
by adkilla on Sat 18th Oct 2008 17:11 in reply to "RE: Defragmentation"
adkilla Member since:
2005-07-07

Yeah, but the question is how much of space? Ext3 currently needs a 30% space requirement to reduce the effects of fragmentation.

Reply Parent Score: 1

RE[2]: Defragmentation
by Morph on Sat 18th Oct 2008 18:45 in reply to "RE: Defragmentation"
Morph Member since:
2007-08-20

You can't break the laws of physics though. If you are going to defragment then you have to have enough free space to move all your files around...

Anyone remember the DOS defrag util that moved around individual clusters? And it displayed a nice big map of the disk showing which sectors it was currenly moving. Free space requirements: one free cluster ;)

Reply Parent Score: 4

RE: Defragmentation
by dimosd on Sat 18th Oct 2008 19:02 in reply to "Defragmentation"
dimosd Member since:
2006-02-10

Is ext4 less prone to performance degradation on filesystems with less space for defragmentation?

I've read that it improves this situation somewhat but no specifics thus far.


I've been using ext4 for the last 3 months (Linux 2.6.26+latest ext4 patch). So far, no problems that me or fsck could detect, so it looks rather stable for a file system in development.

Generally speaking, directory operations (with lots of files) are a lot faster, and so is deleting large files. However, as the disk fills up, performance drops a lot.

Anyway, it is an improvement over ext3 and once it's done I'll probably switch completely to it.

Reply Parent Score: 3