[Novalug] Ext4 != Ext4. Is XFS == XFS?

[James Ewing Cottrell III]

BINGO! It is indeed one of the Features, which can be manipulated by -O 
and -O^ of tune2fs. Specifically, it is the 64bit option:

# e2fsck -f /dev/sda7
sda7 has unsupported feature(s): 64bit

Presumably, I could turn the option off, then fsck it.

Let me state the problem another way. It has been said that there are 
actually 4096 versions of COBOL because there are 12 Optional Features. 
Likewise, with N different Features, there are 2**N different ext4 
filesystems.

One might be tempted to name some of them ext4.rhel5, ext4.rhel6, and 
ext.rhel7 based on the Default Feature Set, but that's not Quite Right 
either, because options may be Turned On and Off at Will, or at least to 
the degree that code supports it.

So how many Options/Features does XFS have? Do RHEL{4,5,6,7} use 
different ones?

So far, I have been using ext4 because that's what I've always done. But 
maybe it's time to Explore a bit. IIRC, isn't it possible to enlarge an 
XFS but not shrink it?

JIM

On 12/9/2016 1:12 PM, Aaron M. Ucko via Novalug wrote:
> James Ewing Cottrell III via Novalug <novalug@firemountain.net> writes:
>
>> What I mean is, if I create an ext4 fs with RHEL6, I can't read it
>> with RHEL6; nor can I read a RHEL6 ext4 fs with RHEL5. The reason is
>> that newer systems use newer features, which are unknown to older
>> systems.
>
> Have you tried adjusting the set of enabled features, via either the -O
> flag or mke2fs.conf?  ext4(5) documents the available choices.
>
> I don't know how XFS compares on this front, but wouldn't be surprised
> if the format remained constant for compatibility with IRIX.
>