Re: A possible direction for the next LVM driver

[Alasdair G Kergon]

On Thu, Aug 30, 2001 at 04:45:47PM +0100, Joe Thornber wrote:
> I'm working on the next iteration of the LVM driver
...which is now known as the "device-mapper" because it lets you define 
new block devices that map I/O onto sections of other block devices.

> The main goal of this driver is to support volume management in
> general, not just for LVM.  The kernel should provide general
> services, not support specific applications.  eg, The driver has no
> concept of volume groups.
 
The latest version being tested is at:
  ftp://ftp.sistina.com/pub/LVM2/device-mapper/device-mapper-0.90.02.tgz
 
The tgz file contains a CVS snapshot which includes patches against 2.4.16
and some documentation (and details for the CVS repository).

Currently there's a choice between an ioctl interface and a filesystem 
interface (dmfs).
 
Example
=======
To create a "logical volume" that concatenates /dev/sdc1 with /dev/sdd2:
[units used below are 512-byte sectors]

# cat > /tmp/lv1_table
0 1028160 linear /dev/sdc1 0
1028160 3903762 linear /dev/sdd2 0
^D
# dmsetup lv1 /tmp/lv1_table

With the filesystem interface and devfs, you could also create 
/devfs/device-mapper/lv1 by hand as follows:

# mkdir /tmp/dmfs; mount -t dmfs dmfs /tmp/dmfs
# mkdir /tmp/dmfs/lv1
# cp /tmp/lv1_table /tmp/dmfs/lv1/table

Striping is also already supported (see documentation).

Alasdair
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