freebsd-dev

History

Jeff Roberson 153910e0f5 - Move the contents of softdep_disk_prewrite into ffs_geom_strategy to fix two bugs. - ffs_disk_prewrite was pulling the vp from the buf and checking for COPYONWRITE, when really it wanted the vp from the bufobj that we're writing to, which is the devvp. This lead to us skipping the copy on write to all file data, which significantly broke snapshots for the last few months. - When the SOFTUPDATES option was not included in the kernel config we would also skip the copy on write check, which would effectively disable snapshots. - Remove an invalid mp_fixme(). Debugging tips from: mckusick Reported by: iedowse, others Discussed with: phk		2005-04-03 10:29:55 +00:00
..
ffs_alloc.c	The recomputation of file system summary at mount time can be a	2005-02-20 08:02:15 +00:00
ffs_balloc.c	For snapshots we need all VOP_LOCKs to be exclusive.	2005-02-08 16:25:50 +00:00
ffs_extern.h	- Move the contents of softdep_disk_prewrite into ffs_geom_strategy to fix	2005-04-03 10:29:55 +00:00
ffs_inode.c	- Fix an assert now that the XLOCK no longer exists.	2005-03-13 12:00:41 +00:00
ffs_rawread.c	- LK_NOPAUSE is a nop now.	2005-03-31 04:37:09 +00:00
ffs_snapshot.c	- Set LK_NOSHARE for snapshot locks. snapshots require exclusive only	2005-03-31 05:21:17 +00:00
ffs_softdep.c	- Move the contents of softdep_disk_prewrite into ffs_geom_strategy to fix	2005-04-03 10:29:55 +00:00
ffs_subr.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
ffs_tables.c	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00
ffs_vfsops.c	- Move the contents of softdep_disk_prewrite into ffs_geom_strategy to fix	2005-04-03 10:29:55 +00:00
ffs_vnops.c	- Set LK_NOSHARE for snapshot locks. snapshots require exclusive only	2005-03-31 05:21:17 +00:00
fs.h	The recomputation of file system summary at mount time can be a	2005-02-20 08:02:15 +00:00
README.snapshot
README.softupdates
softdep.h	/* -> /*- for license, minor formatting changes	2005-01-07 02:29:27 +00:00

README.softupdates

$FreeBSD$

Using Soft Updates

To enable the soft updates feature in your kernel, add option
SOFTUPDATES to your kernel configuration.

Once you are running a kernel with soft update support, you need to enable
it for whichever filesystems you wish to run with the soft update policy.
This is done with the -n option to tunefs(8) on the UNMOUNTED filesystems,
e.g. from single-user mode you'd do something like:

	tunefs -n enable /usr

To permanently enable soft updates on the /usr filesystem (or at least
until a corresponding ``tunefs -n disable'' is done).


Soft Updates Copyright Restrictions

As of June 2000 the restrictive copyright has been removed and 
replaced with a `Berkeley-style' copyright. The files implementing
soft updates now reside in the sys/ufs/ffs directory and are
compiled into the generic kernel by default.


Soft Updates Status

The soft updates code has been running in production on many
systems for the past two years generally quite successfully.
The two current sets of shortcomings are:

1) On filesystems that are chronically full, the two minute lag
   from the time a file is deleted until its free space shows up
   will result in premature filesystem full failures. This
   failure mode is most evident in small filesystems such as
   the root. For this reason, use of soft updates is not
   recommended on the root filesystem.

2) If your system routines runs parallel processes each of which
   remove many files, the kernel memory rate limiting code may
   not be able to slow removal operations to a level sustainable
   by the disk subsystem. The result is that the kernel runs out
   of memory and hangs.

Both of these problems are being addressed, but have not yet
been resolved. There are no other known problems at this time.


How Soft Updates Work

For more general information on soft updates, please see:
	http://www.mckusick.com/softdep/
	http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/

--
Marshall Kirk McKusick <mckusick@mckusick.com>
July 2000