Features/F17Ext4Above16T

= Ext4 support beyond 16T =

Summary
Support Ext4 filesystems larger than 16 terabytes.

Owner

 * Name: Eric Sandeen


 * Email: sandeen@redhat.com

Current status

 * Targeted release: Fedora 17
 * Last updated: 09 Jan 2012
 * Percentage of completion: 80%

Detailed Description
Previous Fedora releases have been limited to 16T (or more exactly, 2^32 filesystem blocks) maximum filesystem sizes on ext4. The recent e2fsprogs-1.42 release upstream has lifted this limitation, and the desire is to scale ext4 to 100T maximum filesystem size. While code is generally in place, testing and verification will be useful.

Benefit to Fedora
16T is also known as "A raid of a few cheap commodity 3T drives" and is just not that big today. Users will be running into the 16T limits of Ext4, and while Fedora ships non-default filesystems like XFS which can handle this without any trouble, we should improve our default filesystem to function at these sizes as well.

Scope
e2fsprogs-1.42 has already been released with initial support greater than 16T, and kernel code already has support as well. There are rough edges to work out, and there is testing to be done.

How To Test
Ideally, stress testing on actual storage of significant size. However, we can also make use of things like sparse loopback files or dm targets to facilitate testing when large storage is not available. The xfstests test suite can do some work on large loopback files, for example.

User Experience
No significant changes, other than the ability to mkfs, mount, and administer larger ext4 filesystems.

Dependencies
None.

Contingency Plan
If significant issues are encountered, we could locally patch e2fsprogs-1.42 and beyond to disallow larger filesystems.

Documentation

 * Because this is primarily an enhancement of existing capability, very little documentation should be required, unless we run into significant caveats for use.

Release Notes

 * Ext4 filesystems are now capable of greater than 16T.

Comments and Discussion

 * See Talk:Features/F17Ext4Above16T