On May 4, 2018, at 9:04 PM, Niklas Hambüchen <mail@xxxxxx> wrote: > > Hello, > > The article https://raid6.com.au/posts/fs_ext4_external_journal_caveats/ > is an often-cited source about setting up external journals. > > It claims that without the `journal_async_commit` mount option ext4 with > external journal will eventually go read-only. > >> Apparently external journal can't be updated in synchronous manner so >> sooner or later ext4 switches to read-only mode following journal commit >> error. > > https://www.arm-blog.com/ext4-journal-nvram-card/ makes the same claim. > >> The “journal_async_commit” is mandatory in order to use the external >> journal. If you forget to mount the filesystem with this flag it >> eventually become read-only and will need a diskcheck before you can >> mount it again! This problem occurs because the external journal cannot >> sync in synchronised mode. This second report is just a repeat of the first one (it even links to the earlier article). > But the only upstream bugs I could find are records of situations where > _with_ the option ext4 went read-only at boot or remount. > > Is the issue described in these articles a known problem? In any case, I couldn't find any reports of this causing problems on the linux-ext4 mailing list, which is where it should be reported if anyone has a problem with ext4 (or bugzilla.kernel.org if necessary). If you have the time and a system to test it, you could run with this config with journal_async_commit disabled for some time (with plenty of reboots) and see if you find any problems. That said, if enabling journal_async_commit works for you, then that is the preferred option anyway, since it adds checksums to the journal blocks (which makes for safer recovery), and is also faster. Cheers, Andreas
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