git: HAMMER VFS - Change default from version 3 to version 4
dillon at crater.dragonflybsd.org
Sat Dec 5 09:28:34 PST 2009
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Sat Dec 5 09:20:27 2009 -0800
HAMMER VFS - Change default from version 3 to version 4
* Version 4 is now the default for newfs_hammer and is no longer
considered a work in progress.
* Filesystems may be upgraded to version 4 in-place. The UNDO FIFO
(typically 1G) is reformatted so the upgrade might take a minute or
* Version 4 allows the UNDO FIFO to be flushed without also having
to flush the volume header, removing 2 of the 4 disk syncs typically
required for an fsync() and removing 1 of the 2 disk syncs typically
required for a flush sequence.
This is accomplished by adding a sequence number of the UNDO entries
in the FIFO and preventing them from crossing a 512-byte boundary,
so each 512-byte block starts with an entry. HAMMER's mount code
is then able to scan the UNDO FIFO to determine the start and end
for recovery purposes.
* Version 4 implements the infrastructure needed for REDO, but does not
implement any REDO operations.
Summary of changes:
sys/vfs/hammer/hammer_disk.h | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
DragonFly BSD source repository
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