Quoting "Perry E. Metzger" <perry@piermont.com>:

> It would be very nice to have such a driver. I don't suppose you could
> submit it?

It's been available for a while and I've been using it since.  It probably 
won't work on -current because of changes to the devsw/lkm stuff.  If there's 
really interest to include it, I'd update it to -current and make whatever 
changes are needed/requested.

There's more info in http://mail-index.netbsd.org/netbsd-
users/2003/02/04/0012.html.  The driver is the device-mapper part and it's at 
version 0.03 now.  

I wrote the driver to have Linux LVM2 on NetBSD.  The driver allows to 
implement volume management software entirely in userspace.  It currently 
supports linear and striped (ccd compatible) mapping and I've added some 
limited raid1 support (it always reads on the 1st device and writes to both, 
it's missing scheduling reads on multiple devices, fallback to the mirror on 
error and passing errors up to userspace).  I've also added support for 
device level snapshots, but it has some unresolved issues and I'm not 
pursueing this at the moment since I don't really need the functionality.

Mappings are implemented as source-level and/or LKM-level plugins.  The 
driver is implemented as an LKM for 1.6_STABLE/1.6.1_RC2, tested on i386.  A 
device is configured through a table which defines for ranges of sectors how 
these sectors are mapped to other devices.

Some examples:  A device is created with the dmsetup create command.
The table:
    0 1639008 linear /dev/wd0d 5210352
defines a device equal to this partition in wd0's disklabel:
     e:   1639008   5210352     4.2BSD   1024  8192    86   # (Cyl. 5169 -
6794)
By having multiple lines in the table, sectors can be gathered from several 
places.

The table:
    0 327680 striped 2 32 /dev/wd0m 0 /dev/wd0n 0
defines a device equal to the ccd with the following config:
    ccd0 32 none /dev/wd0m /dev/wd0n
327680 is the total number of sectors on /dev/wd0[mn].

The table:
    0 163840 raid1 2 /dev/wd0m 0 /dev/wd1d 2056576
defines a raid1 on partition wd0m and on sectors 2056576-2220416 on wd1d. 
It's also possible to have more than 1 copy.

-- 
Christian Limpach <chris@pin.lu>