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."

Comments

Sounds like a good idea.

[Ant P.]

This'll fill the gap between now and when Reiser4 is declared stable - some time after Duke Nukem Forever gets released.

Re:Sounds like a good idea.

[Anonymous Coward]

It's BS that people think it should be considered stable. I've never had more corruptions, other than using XFS w/ very heavy writes, than Resier4. It needs at least another year. ext3 on its own, though not awesome in all areas, hasn't lost me any data yet.

Re:Sounds like a good idea.

[CRCulver]

This'll fill the gap between now and when Reiser4 is declared stable

Reiser4 will never be declared stable in the Linux kernel because Hans Reiser refuses to make his code conformant to kernel coding standards. There has been long and wearying discussion of this on the LKML.

Re:Sounds like a good idea.

[mnmn]

Who cares? Linux has more than its fair share of filesystems, including XFS. I'm still wondering why XFS isnt used universally on desktop and server Linux installations everywhere. Is the ext2/3 just 'traditional'?

Re:Sounds like a good idea.

[raxx7]

There are or were a few quirks.

First off the bat: you can't install the bootloader in a XFS partition since XFS uses the first 512 byte block on the partition. Of course, most people install the bootloader in the MBR but for some it's an issue.

GRUB had a bug with XFS. When you tried to use a XFS partition as /boot, you could corrupt XFS.

For a considerable period of time, ext3's code was more stable than XFS.

ext3 has an ordered data mode (which is the default). Other journaled file systems only support writeback mode. In general, ordered data mode doesn't provide any better warranty of consistency than writeback mode but does make an important difference for a few special cases but which can make a substancial difference to a desktop user.

Typical annoying case:
- You're editing a file on your favorite text editor and you save it.
- The editor opens the file in overwrite mode, meaning the file is actually deleted and a new one is created (under Linux's default settings, the OS will commit the changes to the metadata in 5 seconds or less and the changes to the data in 30 seconds or less).
- The changes to the metadata are commited to disk.
- The system crashes!
When the system comes back up, the new file is there it's full of garbage.

With ext3's ordered data mode, the contents of the file would have been commited to disk before the associated changes to metadata. It's problable (but not assured!!) that after a crash you'll have either the old version or the new version of the file.

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).

Re:Sounds like a good idea.

[szap]

Just a quick chime in, take it with a grain of salt. Some rambling thoughts.

I've just converted my main partition (non-/boot) on a notebook from XFS to reiser3 mainly because I work with huge svn working copies and svn loves to keep small files around, as well as create lots of small files (lock files, etc) during routine svn work. xfs is just way considerably slower than reiserfs for svn status, update, commit, cleanup. Besides, reiser3's tail feature means svn's penchant for small files uses less space overall on my tinny notebook harddrive. Not sure if performance of reiser3 will degrade over time, (I've been on xfs on this partition for longer than a year), but we'll see.

BTW, http://www.debian-administration.org/articles/388 My observations differ from theirs (operations on file tree). I do have a significant larger amount of files, and many of those are smaller than the default block size, so that might affect things.

On the server side, XFS, on multiple concurrent large, random, writes (postgresql) just creams reiser3 and ext3. (IIRC, battery backed SCSI raid controller, tested with both RAID1+0 and RAID5, Linux 2.6.x, 6 x 15000RPM 132(?)GB HDD) Read operations and single thread seq/random writes are too similar in performance for the various filesystems.

Another feature of XFS I used a lot (before converting to reiser3) is xfs_fsr, which defrags a mounted xfs filesystem. Oddly buggy though, as after some runs, some inodes tends to have max_extents corrupted (endian problem?). I'd recommend a xfs_repair after a xfs_fsr, which effectively makes xfs_fsr a utility for defragging *UN*mounted filesystems. So yeah, xfs is a tad unstable. I've only one real corruption, though, and that's from killing the notebook power during some writes. Not sure if that's from the fs, or the harddisk misbehaving.

Re:Sounds like a good idea.

[hansreiser]

What are you talking about? I said I didn't like the coding standards. I then had us change the code to conform to them.

Re:Sounds like a good idea.

[fbjon]

But if the code's already been changed, why hasn't it been included yet?

Yes but

[Anonymous Coward]

Yes, but will it be enough if you had energy to boil all the oceans?

Interesting bit from wiki/ZFS:

ZFS is a 128-bit file system, which means it can provide 16 billion billion times the capacity of current 64-bit systems. The limitations of ZFS are designed to be so large that they will never be encountered in any practical operation. When contemplating the capacity of this system, Bonwick stated "Populating 128-bit file systems would exceed the quantum limits of earth-based storage. You couldn't fill a 128-bit storage pool without boiling the oceans."

In reply to a question about filling up the ZFS without boiling the ocean, Jeff Bonwick, an engineer at Sun Microsystems who led the team in developing ZFS for Solaris, offered this answer:

"Although we'd all like Moore's Law to continue forever, quantum mechanics imposes some fundamental limits on the computation rate and information capacity of any physical device. In particular, it has been shown that 1 kilogram of matter confined to 1 liter of space can perform at most 1051 operations per second on at most 1031 bits of information [see Seth Lloyd, "Ultimate physical limits to computation." Nature 406, 1047-1054 (2000)]. A fully-populated 128-bit storage pool would contain 2128 blocks (nibbles) = 2137 bytes = 2140 bits; therefore the minimum mass required to hold the bits would be (2140 bits) / (1031 bits/kg) = 136 billion kg.

To operate at the 1031 bits/kg limit, however, the entire mass of the computer must be in the form of pure energy. By E=mc2, the rest energy of 136 billion kg is 1.2x1028 J. The mass of the oceans is about 1.4x1021 kg. It takes about 4,000 J to raise the temperature of 1 kg of water by 1 degree Celsius, and thus about 400,000 J to heat 1 kg of water from freezing to boiling. The latent heat of vaporization adds another 2 million J/kg. Thus the energy required to boil the oceans is about 2.4x106 J/kg * 1.4x1021 kg = 3.4x1027 J. Thus, fully populating a 128-bit storage pool would, literally, require more energy than boiling the oceans."

Re:Yes but

[Anonymous Coward]

That post makes more sense if you realize that there should be ^ marks to show exponentiation, such as 10^51 and 2^140. Otherwise it just looks like gibberish numbers that someone made up and stuck in the wiki for shits and giggles.

Re:Yes but

[Anonymous Coward]

Nature 406, 10^47-10^54 (2000)

Volume 406 is really thick.

LWN article on ext4

[ElMiguel]

LWN had an interesting article on ext4 not long ago.

Modularizable filesystem

[Square Snow Man]

What about a modularizable filesystem, which can be upgraded with modules for compression, encryption, larger file support etc. ? Is this impossible or is it a unkown area for the linux developers?

Re:Modularizable filesystem

[Bogtha]

Reiser4 does this.

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: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 is what you are after, but I doubt it.

Re:Modularizable filesystem

[CastrTroy]

However, a kernel which didn't support EXT3 could still read and write EXT3. EXT 3 is completely backwards compatible with EXT2. While you're running in EXT2 mode, none of the journalling stuff is done, but the data can still be read and written. Then you can unmount, and remount the drive as EXT3, and everything will be fine. At least that's my understanding. This might be harder to do with certain features. You can't just ignore encryption. Especially when trying to read data.

ClusterFS

[schon]

engineers from Red Hat, ClusterFS, IBM

OK, hands up - who wants to run ClusterFS so that they can say they needed to do a "clusterfsck"?

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: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:define very large

[runep]

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

I think you underestimate the combination of lonely geeks, OCD, unemployment, broadband and wget.

Re:define very large

[zlogic]

Though this may be needed in some rare applications, I don't see ext4 as something needed in the near future. As I understand, the larger the max partition&file size, the more space indexes will need (not to mention that speed will probably drop).
For example, if we have 20-bit indexes (2^20 clusters max) and use 4-kilobyte clusters, to increase the maximum space we'll either have to add one bit to the indexes to double the maximum space or we'll have to increase the cluster size and have problems storing small files (remember the FAT16->FAT32 transition?)
ext4 is thousands larger than ext3, which will probably mean that indexes will need a lot more space, which will be bad for 8TB volumes (and besides, noone would notice any benefits!)

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).

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").

Re:define very large

[Kjella]

From what I understood the sector index will be configurable as either 32 or 64 bit, so pick it if you need it... Since there's no reason to use it unless the disk is that big, I imagine this can be set automaticly. Also, the whole reason this will be ext4 is that they'll change the way it stores the sectors (ranges instead of singles) which will be better for big files, and since one sector is 4kB almost any file is "big".

LKML Message

[Anonymous Coward]

The kernel mailing list message:

Subject Proposal and plan for ext2/3 future development work
From "Theodore Ts'o"
Date Wed, 28 Jun 2006 19:55:39 -0400

Given the recent discussion on LKML two weeks ago, it is clear that many
people feel they have a stake in the future development plans of the
ext2/ext3 filesystem, as it one of the most popular and commonly used
filesystems, particular amongst the kernel development community. For
this reason, the stakes are higher than it would be for other
filesystems. The concerns that were expressed can be summarized in the
following points:

* Stability. There is a concern that while we are adding new
features, bugs might cause developers to lose work.
This is particularly a concern given that 2.6 is a
"stable" kernel series, but traditionally ext2/3
developers have been very careful even during
development series since kernel developers tend to get
cranky when all of their filesystems get trashed.

* Compatibility confusion. While the ext2/3 superblock does
have a very flexible and powerful system for
indicating forwards and backwards compatibility, the
possibility of user confusion has caused concern by
some, to the point where there has been one proposal
to deliberately break forwards compatibility in order
to remove possible confusion about backwards
compatibility. This seems to be going too far,
although we do need to warn against kernel and
distribution-level code from blindly upgrading users'
filesystems and removing the ability for those
filesystems to be mounted on older systems without an
explicit user approval step, preferably with tools
that allow for easy upgrading and downgrading.

* Code complexity. There is a concern that unless the code is
properly factored, that it may become difficult to
read due to a lot of conditionals to support older
filesystem formats.

Unfortunately, these various concerns were sometimes mixed together in
the discussion two months ago, and so it was hard to make progress.
Linus's concern seems to have been primarily the first point, with
perhaps a minor consideration of the 3rd. Others dwelled very heavily
on the second point.

To address these issues, after discussing the matter amongst ourselves,
the ext2/3 developers would like to propose the following path forward.

1) The creation of a new filesystem codebase in the 2.6 kernel tree in /usr/src/linux/fs/ext4 that will initially register itself as the
"ext3dev" filesystem. This will be explicitly marked as an
CONFIG_EXPERIMENTAL filesystem, and will in affect be a "development
f

Re:How does it compare to zfs?

[Ignominious Cow Herd]

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

Why EXT4 ?

[Anonymous Coward]

Ext4 is an extention of ext3, much like ext3 is an extention of ext2. The plan is to ensure backwards compatability and sanity for when things break, and with filesystems.. things break.

There are many factors that influence filesystems, not just "how fast it can write", but rather.. how it breaks when it does.

While the fanboys of XFS, JFS, ZFS may promise that their filesystems are faster, had no problems, secure and will not eat your data, it simply is not as proven as ext2 and ext3.

Scream fanboys scream, someone will listen, but the problem is that these filesystems are not proven in the field, or in some circumstances even in the kernel itself.

Re:Why EXT4 ?

[Frumious Wombat]

Actually, XFS (SGI), JFS (IBM), and ZFS (Sun) are very well proven in the field, on their respective native operating systems. Given the situations they're used in (financial sector, pharmaceutical research data, supercomputing), they're far more proven that EXT(anything). Now, whether the average Linux user knows how to install, tune, and use them is a different issue, but if I were worried about scalable, mission-critical, filesystems, those three would be on the top of my list. (and my personal history says that while XFS never gave me any trouble, JFS would be my first choice. Nobody ever let me have a budget large enough to buy a machine that would justify ZFS).

With IBM's know-how in the mix, EXT4 may be able to join the above three, but it would seem to be time better spent fixing XFS/JFS support in Linux first, rather than worrying about backwards compatibility with EXT2.

Re:Why EXT4 ?

[Znork]

"ZFS (Sun) are very well proven in the field"

Um, I have yet to see a production installation of ZFS in an enterprise environment, and it hasn't been out as an actual release for even a year yet. You probably mean UFS. HTH.

Re:Why EXT4 ?

[Carewolf]

In enterprise.. Exactly!

Note that servers with extensive mirroring and other hardware error-handling rarely need error-recovery from the filesystem. Filesystem errors happen on ordinary peoples harddrives when they grow old, and ext* have a million times more experience in the handling those than any enterprise FS..

Re:Why EXT4 ?

[Builder]

Actually, I think you'll find that ZFS has been out as a production release (GA or Generally available) for just under 2 weeks now. That's weeks!

There is no way in hell that ZFS is even _remotely_ proven in the field. And since we're still fighting with a bug with Sun Disksuite where you can't boot off the second disk when a disk in a mirror breaks, I'd be VERY loathe to mention Sun, Filesystems and Disk management as being stable right now.

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."

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:Why only 48 bits?

[r00t]

With a block size of 32 kB (64 kB is expected to be supported soonish) the 48-bit numbers will take you 1 byte over the maximum file size that apps can support. There is no UNIX-like OS that lets an app handle files bigger than 2**63.

We'll need to adjust other things if filesystems ever get so huge. The whole design probably needs a rethink, but we can't do it now. We don't know what the future holds in terms of seek times, transfer rates, sector sizes, etc.

128 bits?

[turgid]

"128 bits should be enough for anyone." - Scott G. McNealy (retired).

/me ducks.

Re:128 bits?

[maxwell demon]

Well, let's see what you can address with 128 bits. If we assume byte-addressing, it's enough for 2^128=3.4*10^38 bytes, or 2.7*10^39 bits.

Now lets assume we want to store every bit in a single carbon atom. Carbon has a specific mass of 12 g/mol, 1 mol about 6.022*10^23 atoms. So 2.7*10^39 bits would translate to 4.5*10^15 mol, or 5.4*10^16 g, which is 54 gigatonnes of carbon.

I doubt hard drives will get larger than that any time soon :-)

Pattern

[Eudial]

Ext2...Ext3...Ext4

Wait... I think I can detect a pattern. The next number has to be Ext7½!

fsck quality

[r00t]

Nobody has a fsck that can compare to e2fsck (ext2/ext3/etc.) for quality.

The e2fsck program has a huge test suite that it must pass before a release. A set of corrupted filesystems must be correctly repaired to be bit-for-bit identical to the desired result.

A typical fsck has a good chance of crashing (SIGSEGV, the "segmentation violation") when the going gets tough.

While FreeBSD's UFS developers were messing around with sync writes to avoid testing a fsck that would often crash, the ext2 developers ran full async and wrote a damn fine fsck to put things back in order. Now you can choose from three different levels of journalling, and you still get the ass-kicking fsck program.

There basically is no fsck for XFS, Reiserfs, or Reiser4. JFS doesn't have much AFAIK, and ZFS is a newborn.

What are you going to do when your fancy filesystem gets trashed? I hope you keep excellent backups, very recent and tested to be readable.

Re:fsck quality

[TarpaKungs]

Nonsense. xfs_repair runs over half a dozen checks on metadata. I've done it and watched it and it is thorough. The only problem is running it on 32 bit architectures with a 13TB filesystem, when it runs out of memory address space at around phase 7. That's curable with an Operton.

Re:fsck quality

[hansreiser]

ext2fsck has a history of plenty of problems, just like everyone. I get reports from users swearing they will never again use ext*. Ted Tso goes walking around FUD'ing everyone else's fsck. He does this because ext* performance is poor, so there is not much else to do but FUD. Some users suspect that high performance is a little sinful, so this works on some.

All of the major filesystems have a decent fsck, and all of them are by now stable to the point that you should worry about your hardware and backups failing, not your FS. The only qualifier on that is that ZFS is new, and I hope no one will view that as my FUDing.

Yes.

[r00t]

The new data structures take up less space. They are thus faster to write and faster to read. They also seem to make delayed allocation easier.

Well, how does a Honda Civic ...

[tetromino]

compare to a Liebherr T282? 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:Well, how does a Honda Civic ...

[DavidS]

This is simply not true. ZFS is not just for big iron. It's strongest feature is perhaps the melding of the volume manager and raid into one single unit greatly simplifies administration. Not to mention other nice features, either new os greatly simplified from their past versions, such as pooling, dynamic striping, CoW, instant snapshots and cloning, fault tolerance, etc.

I'd suggest reading through these links before spreading more mis-information:

http://unixconsult.org/zfs_vs_lvm.html - ZFS vs. Linux Raid vs. Linux LVM vs. Linux LVM + Raid

http://uadmin.blogspot.com/2006/05/why-zfs-for-hom e.html - Why ZFS for home

dks

Re:Well, how does a Honda Civic ...

[DavidS]

This is true, but let's look at the case of 1-2 drives:

Assuming we still want mirroring or volume management on our two drives:
The overhead is still greater for SVM or for linux md and sistina lvm. Both require more administration knowledge, time, and commands to accomplish the same tasks that ZFS can do in a couple commands. (Yes, I'm aware that mdadm helps the process a *bit*, but it's still obtuse.) Anyone who has setup either knows how annoying anything is with either choice. (having to micromanage partitions, etc.)

The biggest thing for ZFS in a ``small'' 1-2 drive usage case is, in my opinion, the pooling: ZFS doesn't require one to set volume sizes in advance. Since everything pulls out of a common pool, the size of volumes can grow or shrink accordingly. (Affected by free pool space or volume quotas.) So, that means that one can just create their volumes, and not have to worry about making them the wrong size.

I'd also argue that fault tolerance is important anywhere, large or small.

Another thing is on-disk, low overhead, compression that can be enabled just by toggling one filesystem paramater, live. For a lot of things that people store, this compression would save a lot of space.

They really put a lot of thought in ZFS. It scales amazingly well, from small to large. I'm not really giving it justice explaining it here, so I'd encourage you to look at the documentation with an open mind before just writing it off as an ``enterprise only'' thing.

dks
(I have no affiliation with Sun in any way.

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.

A real O/S filesystem needs defrag!

[ArtStone]

The main described change / advantage in this proposed ext4 is that the notion that a file's allocation is tracked via "extents" (a specified number of contiguous 2k blocks) rather than a chain of inode pointers (with up to 3 levels of indirection).

This is based not only on the need for a larger maximum file system, but a recognition that there is significant performance advantage to reducing read/write head movement and initiating large reads from consecutive blocks that can take advantage of the high transfer rates of today's drives. (this assumes that the OS filesystem doesn't attempt/require that the entire disk drive be cached in RAM to get decent performance)

Except for "write once" files, over time this will cause files to become physically spread over the disk and the performance benefit is reduced, unless a process periodically consolidates the blocks back into a contiguous series of blocks (ignoring for the moment that on today's disk drives, blocks may be "spared" into place that are not really physically consecutive, but just logically appear to be)...

One of the "proofs" that *nix is superior to other O/Ss has been the absence of a need to "Defrag" the file system.

A commenter on the article also raises the question of why the "right" solution isn't to increase the 2k block size limit rather than rework the internals of the block pointers, and got the response that since the linux kernal manages memory in 2k blocks, it is a nightmare in the kernal to support larger I/O transfers (although others here seem to indicate this is one of the solutions people have implemented)

Isn't "extents" a concept contained in NTFS? Has anyone looked into the patent implications of these proposed changes?