What is the difference between ext3 and ext4 in linux

In addition, the Delayed allocation feature could trigger potential data loss when a system crash or power failure occurs before the data has been written to disk. After reading the above information, I believe that you already have known the answer. Ext2 vs Ext3 vs Ext4: which one should you use?

A lot of people are still confused about this question. If you are not sure, the Ext4 file system is an ideal choice. At present, Ext4 is the default file system for most Linux distributions including Debian and Ubuntu. It provides more flexibility for storing large files and boasts more advanced features than the other two extended file systems. In addition, Ext4 was designed to be backward compatible. It has more advantages over reducing file fragmentation, improving flash memory life, and storing large files than Ext2 and Ext3.

How to do that? It is highly recommended that you use MiniTool Partition Wizard. Step 1. Press the buttons below to download MiniTool Partition Wizard and launch it. Free Download. Step 2. In the main interface, and then select the unallocated space and click on Create Partition from the left pane. Step 3. Then click on OK to save the changes. This post analyzes the differences on Ext2 vs Ext3 vs Ext4 comprehensively. Are you also trying to figure it out? This post is what you need. Click to tweet.

Here comes the end of this post. Now, you should have known the differences between Ext4 vs Ext3 vs Ext2.

If you are not sure which one to choose, we recommend you use Ext4. Ext3, and other filesystems of the late s, such as Microsoft's NTFS, uses journaling to solve this problem. The journal is a special allocation on disk where writes are stored in transactions; if the transaction finishes writing to disk, its data in the journal is committed to the filesystem itself.

If the system crashes before that operation is committed, the newly rebooted system recognizes it as an incomplete transaction and rolls it back as though it had never taken place. This means that the file being worked on may still be lost, but the filesystem itself remains consistent, and all other data is safe. Three levels of journaling are available in the Linux kernel implementation of ext3: journal , ordered , and writeback.

Like ext2 before it, ext3 uses bit internal addressing. This means that with a blocksize of 4K, the largest filesize it can handle is 2 TiB in a maximum filesystem size of 16 TiB. Theodore Ts'o who by then was ext3's principal developer announced ext4 in , and it was added to mainline Linux two years later, in kernel version 2. Ts'o describes ext4 as a stopgap technology which significantly extends ext3 but is still reliant on old technology.

He expects it to be supplanted eventually by a true next-generation filesystem. Ext4 is functionally very similar to ext3, but brings large filesystem support, improved resistance to fragmentation, higher performance, and improved timestamps. Ext4 was specifically designed to be as backward-compatible as possible with ext3.

This not only allows ext3 filesystems to be upgraded in place to ext4; it also permits the ext4 driver to automatically mount ext3 filesystems in ext3 mode, making it unnecessary to maintain the two codebases separately.

Ext3 filesystems used bit addressing, limiting them to 2 TiB files and 16 TiB filesystems assuming a 4 KiB blocksize; some ext3 filesystems use smaller blocksizes and are thus limited even further.

Ext4 uses bit internal addressing, making it theoretically possible to allocate files up to 16 TiB on filesystems up to 1,, TiB 1 EiB. Ext4 introduces a lot of improvements in the ways storage blocks are allocated before writing them to disk, which can significantly increase both read and write performance.

An extent is a range of contiguous physical blocks up to MiB, assuming a 4 KiB block size that can be reserved and addressed at once. Utilizing extents decreases the number of inodes required by a given file and significantly decreases fragmentation and increases performance when writing large files.

Ext3 called its block allocator once for each new block allocated. This could easily result in heavy fragmentation when multiple writers are open concurrently. However, ext4 uses delayed allocation, which allows it to coalesce writes and make better decisions about how to allocate blocks for the writes it has not yet committed. When pre-allocating disk space for a file, most file systems must write zeroes to the blocks for that file on creation.

Ext4 allows the use of fallocate instead, which guarantees the availability of the space and attempts to find contiguous space for it without first needing to write to it. This significantly increases performance in both writes and future reads of the written data for streaming and database applications.

This is a chewy—and contentious—feature. Delayed allocation allows ext4 to wait to allocate the actual blocks it will write data to until it's ready to commit that data to disk. By contrast, ext3 would allocate blocks immediately, even while the data was still flowing into a write cache. Delaying allocation of blocks as data accumulates in cache allows the filesystem to make saner choices about how to allocate those blocks, reducing fragmentation write and, later, read and increasing performance significantly.

Unfortunately, it increases the potential for data loss in programs that have not been specifically written to call fsync when the programmer wants to ensure data has been flushed entirely to disk.

With legacy filesystems, close fd ; is sufficient to guarantee that the contents of file will be flushed to disk. Even though the write is not, strictly speaking, transactional, there's very little risk of losing the data if a crash occurs after the file is closed. If the write does not succeed due to errors in the program, errors on the disk, power loss, etc.

If other processes access the file as it is being written, they will see a corrupted version. And if other processes have the file open and do not expect its contents to change—e. Instead, they might write to a new file, close it, then rename it over the old one:.

Under filesystems without delayed allocation, this is sufficient to avoid the potential corruption and crash problems outlined above: Since rename is an atomic operation, it won't be interrupted by a crash; and running programs will continue to reference the old, now unlinked version of file for as long as they have an open filehandle to it.

But because ext4's delayed allocation can cause writes to be delayed and re-ordered, the rename "newfile","file" may be carried out before the contents of newfile are actually written to disk, which opens the problem of parallel processes getting bad versions of file all over again.

To mitigate this, the Linux kernel since version 2. This reduces, but does not prevent, the potential for data loss—and it doesn't help at all with new files. If you're a developer, please take note: The only way to guarantee data is written to disk immediately is to call fsync appropriately. Ext3 was limited to a total of 32, subdirectories; ext4 allows an unlimited number. Beginning with kernel 2. Ext3 did not checksum its journals, which presented problems for disk or controller devices with caches of their own, outside the kernel's direct control.

If a controller or a disk with its own cache did writes out of order, it could break ext3's journaling transaction order, potentially corrupting files being written to during or for some time preceding a crash. In practice, it's been discovered that storage devices and controllers frequently do not honor write barriers—improving performance and benchmarks, where they're compared to their competitors but opening up the possibility of data corruption that should have been prevented.

Checksumming the journal allows the filesystem to realize that some of its entries are invalid or out-of-order on the first mount after a crash. This thereby avoids the mistake of rolling back partial or out-of-order journal entries and further damaging the filesystem—even if the storage devices lie and don't honor barriers. Under ext3, the entire filesystem—including deleted and empty files—required checking when fsck is invoked.

By contrast, ext4 marks unallocated blocks and sections of the inode table as such, allowing fsck to skip them entirely. This greatly reduces the time to run fsck on most filesystems and has been implemented since kernel 2.

Ext3 offered timestamps granular to one second. While sufficient for most uses, mission-critical applications are frequently looking for much, much tighter time control.

Ext4 makes itself available to those enterprise, scientific, and mission-critical applications by offering timestamps in the nanoseconds. Ext3 filesystems also did not provide sufficient bits to store dates beyond January 18, Ext4 adds an additional two bits here, extending the Unix epoch another years.

If you're reading this in AD, you have hopefully already moved onto a better filesystem—but it'll make me posthumously very, very happy if you're still measuring the time since UTC , January 1, Neither ext2 nor ext3 directly supported online defragmentation—that is, defragging the filesystem while mounted. Ext2 had an included utility, e2defrag , that did what the name implies—but it needed to be run offline while the filesystem was not mounted.

This is, obviously, especially problematic for a root filesystem. The situation was even worse in ext3—although ext3 was much less likely to suffer from severe fragmentation than ext2 was, running e2defrag against an ext3 filesystem could result in catastrophic corruption and data loss. Although ext3 was originally deemed "unaffected by fragmentation," processes that employ massively parallel write processes to the same file e. Several userspace hacks and workarounds, such as Shake , addressed this in one way or another—but they were slower and in various ways less satisfactory than a true, filesystem-aware, kernel-level defrag process.

Ext4 addresses this problem head on with e4defrag , an online, kernel-mode, filesystem-aware, block-and-extent-level defragmentation utility. Ext4 is, as the Monty Python plague victim once said, "not quite dead yet! In ext4, you also have the option of turning the journaling feature off.

I myself have had zero problems with ext4. Improve this answer. Matthias Braun 7 7 silver badges 16 16 bronze badges.

Rinzwind Rinzwind k 37 37 gold badges silver badges bronze badges. I tend to use a USB stick for that. Copy to stick and data is available on other OS'es.

Journalling is generally a good thing. Only turn it off if you know exactly what you are doing. Windows 10 and QTS 4. You are looking at a samba share. Not directly on ext4. Show 1 more comment. Perkins Perkins 5 5 silver badges 7 7 bronze badges. That "loosing data" problem may occur if you unsafely remove the media. It's comparable with the "Optimize for performance" feature in Windows.

Use the utility called ext2read. That "loosing data" problem, unless it's been fixed, has nothing to do with unsafely removing the medium and everything to do with ext4 taking some assumptions about how the storage device works that aren't true with cheap flash drives. You don't have to remove the medium at all. Just do a big pile of data transfers like, say, installing linux to an ext4 flashdrive. Last time I tried it you'd start getting corrupted and missing files almost before the installation was complete.

And no, there was nothing physically wrong with the drive. It worked fine with ext3. Sign up or log in Sign up using Google.