freebsd-dev

History

Jeff Roberson 8db357205c - Remove the call to softdep_waitidle after suspending the filesystem. This does not do what I wanted as all dirty buffers must be flushed by the call to ffs_sync and any remaining dependency work would mean that this failed. Pointed out by: tegge		2006-03-12 05:26:12 +00:00
..
ffs_alloc.c	- Move softdep from using a global worklist to per-mount worklists. This	2006-03-02 05:50:23 +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	Use vn_start_secondary_write() and vn_finished_secondary_write() as a	2006-03-08 23:43:39 +00:00
ffs_inode.c	- Consistently call 'vp' vp rather than ovp sometimes in ffs_truncate().	2005-04-05 08:49:41 +00:00
ffs_rawread.c	Eliminate a deadlock when creating snapshots. Blocking vn_start_write() must	2006-03-02 22:13:28 +00:00
ffs_snapshot.c	- Remove the call to softdep_waitidle after suspending the filesystem.	2006-03-12 05:26:12 +00:00
ffs_softdep.c	- Remove the call to softdep_waitidle after suspending the filesystem.	2006-03-12 05:24:14 +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	Block secondary writes while expunging active unlinked files.	2006-03-11 01:08:37 +00:00
ffs_vnops.c	Adjust totread argument passed to cluster_read() to account for offset not	2005-10-09 21:11:25 +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	- Move softdep from using a global worklist to per-mount worklists. This	2006-03-02 05:50:23 +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