NOFLUSHD - An idle-disk daemon

This is noflushd, a daemon that spins down disks that have not been read from after a certain amount of time, and then prevents disk writes from spinning them back up. It's for use with kernel versions 2.2.11 and up, where the userland bdflush (update) daemon has been fully integrated in the new kernel thread kupdated (formerly known as kupdate). noflushd uses the sleep support logic from bdflush-1.6.2. bdflush was originally written by Eric Youngdale, Pavel Machek added the sleep support.

FAQ of the CENTURY

Okay, so you're seeing this message trying to start noflushd:

BUG at disk_info.c line 168: Unable to determine device dir
Segmentation fault (core dumped)

This is most probably triggered by one thing: You have compiled the device filesystem (devfs) into the kernel but haven't mounted it (yet). A look into /proc/partitions reveals whether you're running devfs. On a non-devfs kernel, the name field contains entries like hda, sda, hda1, etc. On a devfs kernel, it looks more like ide/host0/bus0/target0/lun0/disc, scsi/host0/bus0/target0/lun0/disc, ide/host0/bus0/target0/lun0/part1, etc.

On a devfs kernel, noflushd absolutely must be able to find the devfs somewhere within the filesystem. In other words, devfs needs to be mounted, or noflushd will BUG. Mounting to /devfs is probably a good idea. So first create the directory:

mkdir /devfs

Then mount devfs on it:

mount -t devfs /devfs

If you want the mount to survive a reboot, add the following to /etc/fstab:

none    /devfs  devfs   defaults        0       0

But of course, this is not your only option. The others being:

You're running a devfs-enabled kernel, so why don't you use it? Install devfsd and boot with devfs=mount. More information on devfs is available at Richard Gooch's site.
Just don't compile devfs in if you don't want to use it.

NEWS

Version 2.7 of noflushd was released on Jan 20th 2004. It is available as a source tarball via http. This release adds support for the 2.6 Linux kernel series, and facilitates configuration on standard setups due to changed default behaviour. Random bug fixes and documentation updates have been supplies as well.

While noflushd ships with an RPM spec file that ought to work on (at least) RedHat and SuSE distribution, the noflushd author is a Debian native and RPM illiterate. RPMs therefore may be considered ill-supported. Matthias Saou, however, provides improved RPMs tailored for recent RedHat systems at freshrpms.net. Unlike the official spec file, his RPMs support persistent configuration data. RedHat users are encouraged to check it out.

Daring folks might be interested in noflushd's bleeding edge version which is now available via anonymous CVS as module noflushd from :pserver:anonymous@cvs.noflushd.sourceforge.net:/cvsroot/noflushd. Just hit return when prompted for a password. There's also a daily CVSROOT snapshot. This is not a ready-to-use tarball, it's the raw repository that you can setup on your local machine.

KNOWN BUGS AND LIMITATIONS

Journaling filesystems like ext3, reiserfs or xfs bypass the kernel's delayed write mechanisms. This amounts to lousy spindown times when working off such a partition. There's no workaround for this.
Due to incompatible changes in the format of /proc/stat, noflushd versions starting from 2.3 will not work on kernels from 2.3.99pre8 to 2.4.0-test8. As these kernels are experimental and obsolete anyway, no attempt will be made to fix this problem. Earlier versions of noflushd will cease to work on kernels 2.4.0-test9 and up. Please consider upgrading.
For further help and information, contact the noflushd mailing list.

RELATED SITES

General project info.
Submit bug reports.
Get bleeding edge snapshots from the CVS repository.
Download noflushd via http or anonymous ftp.
Participate in noflushd development by joining the noflushd-devel mailing list. An online archive is also available.

Yours,
Daniel!

Created: Oct, 28th, 2000 (dk)
Last changed: May, 3rd, 2004 (dk)
Contact: noflushd-devel@lists.sourceforge.net