Date: Fri, 21 Oct 2022 17:57:48 GMT From: Kirk McKusick <mckusick@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 0929a153fc5c - main - Add a description of soft updates journaling to newfs(8). Message-ID: <202210211757.29LHvmc2092890@gitrepo.freebsd.org>
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The branch main has been updated by mckusick: URL: https://cgit.FreeBSD.org/src/commit/?id=0929a153fc5cfe35f7390ab5870a36daed19b0ce commit 0929a153fc5cfe35f7390ab5870a36daed19b0ce Author: Kirk McKusick <mckusick@FreeBSD.org> AuthorDate: 2022-10-21 17:56:20 +0000 Commit: Kirk McKusick <mckusick@FreeBSD.org> CommitDate: 2022-10-21 17:57:31 +0000 Add a description of soft updates journaling to newfs(8). Add a descrition to the newfs(8) -j (journal enablement) flag that explains what soft updates journaling does, the tradeoffs to using it, and the limitations that it imposes. Copied from the description in tunefs(8). PR: 261944 Sponsored by: The FreeBSD Foundation --- sbin/newfs/newfs.8 | 42 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 41 insertions(+), 1 deletion(-) diff --git a/sbin/newfs/newfs.8 b/sbin/newfs/newfs.8 index a5b850c54675..a065563f86d1 100644 --- a/sbin/newfs/newfs.8 +++ b/sbin/newfs/newfs.8 @@ -28,7 +28,7 @@ .\" @(#)newfs.8 8.6 (Berkeley) 5/3/95 .\" $FreeBSD$ .\" -.Dd April 17, 2021 +.Dd October 21, 2022 .Dt NEWFS 8 .Os .Sh NAME @@ -169,6 +169,46 @@ This flag is implemented by running the .Xr tunefs 8 utility found in the user's .Dv $PATH . +.Pp +Enabling journaling reduces the time spent by +.Xr fsck_ffs 8 +cleaning up a filesystem after a crash to a few seconds from minutes to hours. +Without journaling, the time to recover after a crash is a function +of the number of files in the filesystem and the size of the filesystem. +With journaling, the time to recover after a crash is a function of the +amount of activity in the filesystem in the minute before the crash. +Journaled recovery time is usually only a few seconds and never +exceeds a minute. +.Pp +The drawback to using journaling is that the writes to its log adds +an extra write load to the media containing the filesystem. +Thus a write-intensive workload will have reduced throughput on a +filesystem running with journaling. +.Pp +Like all journaling filesystems, the journal recovery will only fix +issues known to the journal. +Specifically if a media error occurs, +the journal will not know about it and hence will not fix it. +Thus when using journaling, it is still necessary to run a full fsck +every few months or after a filesystem panic to check for and fix +any errors brought on by media failure. +A full fsck can be done by running a background fsck on a live +filesystem or by running with the +.Fl f +flag on an unmounted filesystem. +When running +.Xr fsck_ffs 8 +in background on a live filesystem the filesystem performance +will be about half of normal during the time that the background +.Xr fsck_ffs 8 +is running. +Running a full fsck on a UFS filesystem is the equivalent of +running a scrub on a ZFS filesystem. +.Pp +Presently it is not possible to take a snapshot on a UFS filesystem +running with journaled soft updates. +Thus it is not possible to reliably dump mounted filesystems or +to run background fsck on filesystems enabled for journaling. .It Fl k Ar held-for-metadata-blocks Set the amount of space to be held for metadata blocks in each cylinder group. When set, the file system preference routines will try to save
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