EXT4 Is Coming

ah admin writes "A series of patches has been proposed in Linux kernel mailing list earlier by a team of engineers from Red Hat, ClusterFS, IBM and Bull to extend the Ext3 filesystem to add support for very large filesystems. After a long-winded discussion, the developers came forward with a plan to roll these changes into a new version — Ext4."

define very large

[frovingslosh]

OK, I've read both links. What does this mean? Can anyone give a breakdown of ext3 vs. ext4, particularly in terms of what size files and what size partitions they both support, as well as any other differences that can be quantified?

Re:Modularizable filesystem

[dbIII]

Interesting article - the premise that Reiser is more stable than ext3 "because it has been out longer", the quote from Adam Smith, the ridicule of the unix approach of everything as a file and all the naked people covered in newsprint?

Anyone have a "more technical" link without dancing trees and with a bit about how to recover your filesystem when something goes weird with the hardware even if the filesystem is perfect?

Re:define very large

[Kjella]

Let me put it this way, it's a little past the average slashdot porn collection:

ext3: 8TB total, 4TB files
ext4: 32 zettabyte (1024*1024*1024 TB), 1 exabyte files (1024*1024 TB)

Beyond that, it doesn't seem to actually change much.

Re:How does it compare to zfs?

[Ignominious Cow Herd]

Ummm...zfs exists, ext4 doesn't. Yet.

Why only 48 bits?

[The Wicked Priest]

Why not go all the way to 64 bits now, and thereby avoid further changes for the forseeable future? In one of the messages linked from the article, it's suggested that 1024 PB, obscene as it sounds, may only be good enough for another decade.

I guess we'll be on to ext5 or 6 by then, though.

Re:ClusterFS

[Anonymous Coward]

Unfortunately, lustre's fsck is just called lfsck. You run it across the aggregate of file stores making up the cluster filesystem to ensure total consistency, after running clusterfs' e2fsck friendly-fork on each individual object store to ensure local consistency. Most of these changes to ext3 -> ext4 are driven by the needs of Lustre. Lustre FS is basically a virtual filesystem striped across a load of ext3 filesystems on servers. It is blazingly fast and very stable in our tests (clusterfs are _very_ conservative about tagging something "stable", their stuff is used on some serious computers).

Re:Modularizable filesystem

[Bogtha]

the premise that Reiser is more stable than ext3 "because it has been out longer"

It's dishonest to put something in quotes when it's not a direct quote. The exact quote is:

"We don't touch the V3 code except to fix a bug, and as a result we don't get bug reports for the current mainstream kernel version. It shipped before the other journaling filesystems for Linux, and is the most stable of them as a result of having been out the longest. We must caution that just as Linux 2.6 is not yet as stable as Linux 2.4, it will also be some substantial time before V4 is as stable as V3."

There's a substantial difference between saying that something is more stable "as a result" of something and more stable "because" of something. He's not claiming that being out longer intrinsically makes it more stable as your misquote suggests, he's claiming that it led to reiserfs becoming more stable - because of the practices he mentioned.

In short - something being out longer == more stable? No. Something being exposed to lots of real-world use and receiving only bugfixes == more stable? Yes.

the quote from Adam Smith

He didn't quote Adam Smith, he drew an analogy between what he was saying and the network effect. It's an entirely reasonable analogy.

the ridicule of the unix approach of everything as a file

What ridicule? He's actually supporting that approach. For example:

Can we do everything that can be done with {files, directories, attributes, streams} using just {files, directories}? I say yes--if we make files and directories more powerful and flexible. I hope that by the end of reading this you will agree.

Would you care to point out where you thought he was ridiculing the UNIX approach?

all the naked people covered in newsprint

Yeah, they look dumb, don't they?

Anyone have a "more technical" link

I can only assume you mean something other than "technical".

without dancing trees

Dancing trees are a fundamental part of the design. How are you meant to understand the filesystem without understanding dancing trees?

and with a bit about how to recover your filesystem when something goes weird with the hardware even if the filesystem is perfect?

Ah, you don't mean technical at all, you mean practical for somebody who is entirely uninterested in the way the filesystem works. Perhaps Reiser4 Transaction Design Document [namesys.com] is what you are after, but I doubt it.

Well, how does a Honda Civic ...

[tetromino]

compare to a Liebherr T282 [wikipedia.org]? These are two projects with vastly different goals. Ext4 is basically Ext3 with better performance and a much larger maximum capacity; it's still a typical traditional Unix filesystem, a safe default choice for desktops and small servers. ZFS is an exotic beast with a totally ridiculous maximum capacity and tons of advanced of features that do not exist in any other Unix filesystem, but are only useful for Big Iron.

Re:define very large

[glwtta]

ext3: 8TB total, 4TB files
ext4: 32 zettabyte (1024*1024*1024 TB), 1 exabyte files (1024*1024 TB)

Are they just going to work on improving the 8TB paper limitation, or are they actually trying to improve on ext3 scalability? Which, currently tends to suck the big one, especially on a significant number of disks (eg: http://scalability.gelato.org/DiskScalability/Resu lts [gelato.org]).

I also seem to keep coming up against a pretty hard 2TB block device limit in Linux (eg LVM2 lv size, LUN size for fibre attached SAN, etc). I don't really know what the reasons for it are, anyone know what technologies allow for larger single partitions?

Anyway, I've long ago settled on reiserfs (3) for speedy random access to small files, and XFS for file server type applications; though I still wonder why RedHat doesn't include any "enterprise" filesystems by default in their "enterprise" products (I know, I know, you can enable it - I did say "by default").

Linux and other Unix FSes

[digitalhermit]

I'm as big a Linux fan as anyone, but one glaring thing that it needs is some better filesystem tools. Don't get me wrong -- they've come a long way in the last couple years -- but compared to something like AIX it still has a little ways to go. Here's one feature that causes a challenge: Linux filesystems and the underlying logical volume layer is largely decoupled. You have an immense amount of flexibility but as a consequence, the filesystem and volume layers don't always communicate as well. For example, the AIX JFS2 tools allow you to dynamically grow/shrink filesystems. This functionality exists in Linux for some filesystems (EXT3, ReiserFS) but the procedure varies depending on how the filesystem is constructed. And at this point, I'm not fully convinced of its stability as I've recently (three months ago) lost an entire disk after a dynamic resize on an LVM backed EXT3 partition. I have yet to reproduce the failure but it occurred with a 95% full /home and a kernel compile going full tilt.

But I'm amazed at how quickly these features are being integrated. There's functionality in Linux that allows me to easily create file-backed volumes, remote volumes, SAN LUNs, etc.. The "resize in a single command" is not fully there yet, but within 6 months I'd expect it to be.

Re:Linux and other Unix FSes

[Homology]

>I'm as big a Linux fan as anyone, but one glaring thing that it needs is some better filesystem tools.

I'm pretty certain that Linux would have better filesystem tools if the developers could resist add a new filesystem every few months.

Re:My take on current filesystems

[waferhead]

"I consider it to be about as stable as XFS."

I have had my /video and /home partitions on XFS for... WAY too long, several years, same drives.
(I just keep adding on)

I lose power a lot where I live (glitches) and XFS has been utterly bullet proof.

(This filesystem has bee thru 3 motherboards, several linux distros (1 mb dead/2 upgrades), 2 cases, and so on)

If Reiser4 is about as stable as XFS, I'll glady switch everything over tomorrow on my MythTV box.

Re:Why EXT4 ?

[kimvette]

SUN has been using ZFS internally in their enterprise environment for a while.

Most people would not consider that to be "proven in the field"

By your logic, Windows Vista should have been released a year ago because it's long been "proven" stable via widespread deployment at Microsoft.

Internally, Sun has Sun software running mostly on Sun hardware, not the mis-mash of SANs, external and internal third-party hard drives, and custom RAIDs that many enterprises will have. When it's used and stable across a variety of configurations in real-world far-away-from-Sun's-debug-environements without a(n unreasable/unexpected) glitch, it can be considered "proven in the field."

Re:Sounds like a good idea.

[SaDan]

I've read the arguements on LKML, and it seems to me Hans isn't the only one being stubborn about filesystems and whatnot in the kernel. The kernel developers are unyielding to modernizing the VM subsystem, which is causing a lot of grief for ReiserFS.

It's ugly, and annoying, especially for people like me who rely on ReiserFS in production. I'd love to see ReiserFS 4 in the standard kernel, it'd make my life a lot easier.

I can't use EXT2/3, it's too slow and just kills the machine for the amount of files we deal with on a lot of our systems. Going from Ext3 to ReiserFS 3 took us from a machine load of over 50 down to about 3 during stress testing recently.

Hans knows what he's doing, I just wish the kernel developers would accept and respect that (regardless of the retarded ego wars on the LKML).