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I want to use ext4 on my external HDD, but it must be cross-platform. (At least Linux, Win7 & WinXP).

Unfortunately, I haven't found any proper driver allowing Windows to WRITE to ext4. I've found Ext2Fsd, but it only reads ext4.

9. ext4 extent read-only, no size truncating and expanding support

More:

Supported Ext3/4 features:

  • flexible inode size: > 128 bytes, up to block size
  • dir_index: htree directory index
  • filetype: extra file mode in dentry
  • large_file: > 4G files supported
  • sparse_super: super block backup in group descriptor
  • uninit_bg: fast fsck and group checksum
  • extent: reading, writing with no extending.
  • journal: only support replay for internal journal

Unsupported Ext3/4 features:

  • journal: log-based operations, external journal
  • extent: size truncating & expanding, file deletion
  • flex_bg: first metadata group
  • EA (extended attributes), ACL support

Also, I have found a patch for Ext4Fsd v0.50 (here):

New: Matt Wu has made a new release 0.50 at ext2fsd.com. Ext2fsd-0.48-bb8-signed Support for ext4 extents and fix for BSOD on Windows 7.

I don't think it will be safe. Also I've read some words about writing ext4 in Windows could cause data loss on the disk...

What is the External HDD used for? - First, it will store backups, then family movies, pictures. Some music, and etc. It will be connected to a Raspberry Pi, if I finally receive it. It won't really move, just when it is used to migrate computer's data to a new one. The largest files it will store are Clonezilla disk images (I don't know, if they will be large files or not).

Can someone provide a solution for this problem? Or is there NO important enough difference between ext4 and ext3, and I should use ext3? - (If yes, then can I use Ext2Fsd for that ext3 mount?)

Thank you!

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Have a look at this page. I don't think that using ext4 for an external hard drive is worth the headache. Why do you not want NTFS or FAT32? Do you need support for huge files? –  terdon Aug 23 '12 at 15:20
    
Thank you for the link. I forgot add the situation, and aim of the External HDD. Added to the question now. Otherwise, what size do you mean in large files? –  B. Roland Aug 23 '12 at 17:01
    
I agree with terdon. Make the drive NTFS and it will be compatible with most OSs out there. –  Keltari Aug 23 '12 at 17:26
    
One of the many limitations of FAT32 is that it cannot deal with files larger than 4GB. NTFS (16 EB) and ext4 (16 TB) do not have that limitation. –  terdon Aug 24 '12 at 3:54
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3 Answers

up vote 8 down vote accepted

I would use NTFS instead. It can easily be read/written to by Linux, Windows and OS X (among others).

Considering the intended use and the fact that it is an external drive, I see no reason why you should go through the hassle that using ext4 will be.

If this were your primary hard drive, perhaps the advantages of ext4 (briefly, less drive fragmentation and slightly improved performance, for more information see here) would be worthwhile. I doubt you will even notice a difference on an external USB drive. The bottleneck will be the rate of data transfer over the USB cable.

For most users, the only obvious benefit of ext4 over NTFS is that ext4 allows file names with special characters (? & % etc). Such file names, however, are both a bad idea and of no particular interest to you.


EDIT: In answer to B. Roland's question about defragmenting, yes, there are two ways I know of to defragment an NTFS drive under linux. One is an open source tool called shake. I haven't used it but it seems to work. The other is simply copying all data from the external drive, deleting everything from the drive and then copying everything back. Finally, since your drive will also be accessed under windows you can use the windows defragmenter.

I think, however, that you are attaching way too much importance to drive defragmentation. Have a look here for a simple explanation of fragmentation. Briefly, a fragmented drive is one where the files on the drive are not stored in contiguous blocks but spread out across the drive. This is usually caused by changing a file's size after it has been written. So, say you save a 1 MB file on your drive. You then modify the file and its size goes up to 20 MB. If there is not enough free space at the position where the file was created, this extra data will be written to a different part of the hard drive. In other words, the file will be fragmented.

This kind of thing is not likely to occur very often in a drive used for storing "backups, then family movies, pictures. Some music, and etc". Most of these files will never change in size, and therefore, will never fragment the drive.

In addition, even if your drive is fragmented, you don't really care. Fragmentation can be a problem for system drives where you can have many I/O operations per second. In those cases you can notice a decrease in drive performance. As I said before, on an external drive I don't think you will be able to detect this, even if it does happen.

So, in conclusion, you almost certainly will not need to defragment an NTFS formatted external HDD. However, if you really want to, you can do it both in Linux and in Windows.

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I completely agree. NTFS (and FAT32) are simply the most portable file systems out there. –  Keltari Aug 24 '12 at 5:45
    
Will the NTFS worth data fragmentation problem? Ext4 has no fragmentation. Otherwise it has USB 3.0 connector, so it is much faster than a normal USB 2.0. Portability is secondary. It is a WesternDigital My Book Essential (1TB) –  B. Roland Aug 24 '12 at 7:57
    
@B.Roland IMHO, yes. Granted NTFS will have more fragmentation but, again, this should not be a serious problem on an external, non system drive. I really think using ext4 is simply not worth the effort. I very much doubt that you will see any improvement at all. It may be there, but it will probably not even be detectable unless you run benchmarks. I really doubt you will notice any difference as a user. –  terdon Aug 25 '12 at 14:08
    
Oh, ok @terdon, if you add something about how to defragment NTFS on a Linux, I'll accept your answer. (eg. linuxquestions.org/questions/linux-newbie-8/…) –  B. Roland Aug 26 '12 at 8:38
1  
I disagree that it can be easily read/written by all. There's an overhead to ntfs-3g on *nix. –  jhstuckey May 26 '13 at 21:05
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Paragon software offers ExtFS for Windows 2.0 for free for personal use. It allows to read and write ext2 ext3 and ext4 from all Windows OS

http://www.paragon-software.com/home/extfs-windows/

It appears to be somewhat similar to Linux Reader from Diskinternals, that can mount all ext, HFS and ReiserFS too, but read-only.

http://www.diskinternals.com/linux-reader/

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Is Paragon adware/malware free and completely safe? Have you used it yourself? –  Rajib Nov 18 '13 at 15:01
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If you want to SOME of the features of EXT4, you can use them using tune2fs to add the features to an EXT3 partition. The latest Ext2FSD release notes should list which features you can enable. You may want to read the tune2fs man page, there are some hints on how to handle writing to the filesystem in the header that can be beneficial to set for a backup drive that requires reliability, or to set to the other extreme for a drive containing non-critical files that require fast access and fast read-write times

You don't really need extended attributes and ACLs, and depending on your Linux setup they may not even be active to begin with. Incompatibilities between Windows and Linux on permissions makes it ill-advised to use this feature cross platform, even if supported.

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