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bug#46905: Add a note about ext4's dir_index to the manual
From: |
Ludovic Courtès |
Subject: |
bug#46905: Add a note about ext4's dir_index to the manual |
Date: |
Thu, 04 Mar 2021 23:01:26 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) |
Hi!
Tobias Geerinckx-Rice <me@tobias.gr> skribis:
> Mainly a reminder to myself to do so.
>
> Guix can break ext4, and more than once has, with a inscrutable error
> message. We should document it explicitly.
>
> See <http://logs.guix.gnu.org/guix/2021-03-03.log#220037>.
You wrote:
--8<---------------cut here---------------start------------->8---
<nckx>OK, that's the culprit (it's common: ext4 has a design flaw in that it
hashes directory entries and... just
dies when the hash table gets ‘full’). Try ‘tune2fs -E "hash_alg=tea" /dev/foo’
to select a different hash algo, or
‘tune2fs -O "^dir_index" /dev/foo’ to disable it completely if that doesn't
help.
--8<---------------cut here---------------end--------------->8---
Really? I’ve almost always used ‘dir_index’ in my Guix + NixOS days,
and IIRC store accesses were much slower before that was a thing.
On berlin, /gnu is a 37 TiB file system with ‘dir_index’ turned on and
it works well.
I don’t think we can claim there’s a design flaw. WDYT?
Ludo’.