[clug] EXT4 Reliability

[Daniel Pittman]

Anshul Gupta <email.agupta at gmail.com> writes:

> Performance wise ext4 filesystem is better because of extents and persistent
> preallocation which improves performance slightly. Somebody might argue it's
> better for movie files because of contiguous allocation and will wear the
> disk less thereby reduce the risk of disk failure.

Anybody who argued that would, rightly, be looked at very strangely; the
difference that makes in practice is zero, for all practical purposes.

Extents do make access to large data less seek-heavy, though, which can be
a significant performance advantage.

> However I prefer ext3 just because it has been around for many years and
> it's rock solid. Ext4 is still new. Also ext4 filesystem are not as reliable
> due to delayed allocation.

That is a poorly supported statement.  I presume you mean that ext4 has
a higher risk of data loss in the event of a catastrophic system failure, when
faced with incompetently written software.

(Which, sadly, apparently /still/ includes both GNOME and KDE, since both love
 to rewrite their configuration files all too often.  Oh, well.  Maybe that
 got fixed since ext4 made it visible again.)

Anyway, by the time you are having the system hang, panic, or facing power
failures you have more or less already lost in the data integrity stakes;
using ext3 helps, in the same way that stabbing yourself with a *short* skewer
is better than stabbing yourself with a long skewer.

> Also if ext3 disk fails you will find many tools to recover data.

What, debugfs and e2fsck, which also work for ext3 and ext4?  I don't think
you will find substantially changed recovery tools for ext4, generally
speaking.

> That being said, for your important data you should always use some sort of
> RAID.

This doesn't protect you from several of the failure modes of ext4, and can
make things significantly worse by exposing you to additional complexity, and
additional sources of failure.

> And you can always migrate ext3 filesystem to ext4 in future.

...this loses many of the performance benefits, however.

> FAT32 is the most portable filesystem but not as stable and reliable as
> ext[34].

I am surprised you suggest this.  Are you referring to the issues that the FAT
structure introduces WRT the Unix [id]node convention, or the renaming issues,
or something else?

> And using FAT32 filesystem you might not be able to import directly on the
> USB disk as the write speed will be limited by the filesystem. NTFS for
> Linux host doesn't make sense.

This I agree with.


Anyway, personally, if I wanted something faster than ext3 I would look to XFS
which has a much longer history and much better understood failure modes than
the relatively new ext4 — regardless that I have nothing but the highest
respect for the approach, implementation and design of ext4 or its maintainers.

For a backup disk, though, favouring robustness over performance generally
makes sense, so I would likely choose ext3.

        Daniel

Well, I actually chose XFS, but my backup model is quite different from the
one being discussed; external disks just land an xfsdump of the filesystem
snapshot at a suitable time. 

-- 
✣ Daniel Pittman            ✉ daniel at rimspace.net            ☎ +61 401 155 707
               ♽ made with 100 percent post-consumer electrons
   Looking for work?  Love Perl?  In Melbourne, Australia?  We are hiring.