Hello,
I have been considering adding to Linux volume management
capabilities, in the spirit of the IRIX volume management, where it is
possible for a file system to span multiple devices.
Comments on this? Is this proposal completely foolish?
I think the better way to do all this type of stuff is in a block
device driver that presents a virtual block device to the upper
layers. Although I am not fond of Solaris, I think that they may have
done this part right in their online disk suite product.
Basically the way it works is that the metadevice driver gets fed a
configuration of which physical devices it should use and how it
should lay them out to form virtual block devices. Now, the
metadevice driver creates the virtual block devices and registers
them with the block device layer.
Now one can implement many types of disk configurations, concatenated
disks, striped disks, concatenated stripes, concatenated raids,
striped concatenations, whatever. We can probably do logging
filesystems with good extensions to the block device stuff, though I
think that there may be some problems with prioritizing writes in the
buffer cache for the log info.
As long as the metadevice driver can bypass the buffer cache for its
device accesses, things should be ok.
All that needs to be done, then for adding disks to an existing fs, is
to add the physical block device to the virtual block device. Then
write a utility like growext2fs or something that extends the
filesystem beyond the old block limit.
-- Manish Vachharajani <mvachhar@noc.rutgers.edu> Rutgers University http://www-no.rutgers.edu/~mvachhar Telecommunications Division Systems Programmer