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From 3740b7a6d246a5860c8f1d96504bbf00692447e0 Mon Sep 17 00:00:00 2001
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From: Goffredo Baroncelli <kreijack@inwind.it>
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Date: Sun, 12 Apr 2015 20:30:28 +0200
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Subject: [PATCH] tmpfiles: Add +C attrib to the journal files directories
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Add the +C file attribute (NOCOW) to the journal directories, so that
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the flag is inherited automatically for new journal files created in
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them. The journal write pattern is problematic on btrfs file systems as
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it results in badly fragmented files when copy-on-write (COW) is used:
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the performances decreases substantially over time.
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To avoid this issue, this tmpfile.d snippet sets the NOCOW attribute to
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the journal files directories, so newly created journal files inherit
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the NCOOW attribute that disables copy-on-write.
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Be aware that the NOCOW file attribute also disables btrfs checksumming
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for these files, and thus prevents btrfs from rebuilding corrupted files
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on a RAID filesystem.
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In a single disk filesystems (or filesystems without redundancy) it is
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safe to use the NOCOW flags without drawbacks, since the journal files
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contain their own checksumming.
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(cherry picked from commit 3a92e4ba470611ceec6693640b05eb248d62e32d)
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Related: #1299714
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---
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tmpfiles.d/journal-nocow.conf | 27 +++++++++++++++++++++++++++
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1 file changed, 27 insertions(+)
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create mode 100644 tmpfiles.d/journal-nocow.conf
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diff --git a/tmpfiles.d/journal-nocow.conf b/tmpfiles.d/journal-nocow.conf
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new file mode 100644
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index 0000000000..e7938c8911
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--- /dev/null
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+++ b/tmpfiles.d/journal-nocow.conf
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@@ -0,0 +1,27 @@
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+# This file is part of systemd.
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+#
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+# systemd is free software; you can redistribute it and/or modify it
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+# under the terms of the GNU Lesser General Public License as published by
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+# the Free Software Foundation; either version 2.1 of the License, or
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+# (at your option) any later version.
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+
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+# See tmpfiles.d(5) for details
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+
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+# Set the NOCOW attribute for directories of journal files. This flag
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+# is inheredited by their new files and sub-directories. Matters only
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+# for btrfs filesystems.
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+#
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+# WARNING: Enabling the NOCOW attribute improves journal performance
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+# substantially, but also disables the btrfs checksum logic. In
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+# btrfs RAID filesystems the checksums are needed for rebuilding
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+# corrupted files. Without checksums such rebuilds are not
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+# possible.
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+#
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+# In a single-disk filesystem (or a filesystem without redundancy)
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+# enabling the NOCOW attribute for journal files is safe, because
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+# they have their own checksums and a rebuilding wouldn't be possible
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+# in any case.
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+
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+h /var/log/journal - - - - +C
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+h /var/log/journal/%m - - - - +C
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+h /var/log/journal/remote - - - - +C
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