Re: [Xen-devel] Roadmap questions

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> 3) Is there any documentation on the new VBD code?  Is there yet a way
> to make dynamically growing (sparse) disks or to be able to access a
> domain's filesystem from domain 0?

The current generation of VBD stuff is documented in docs/VBD-HOWTO.txt - 
there's some background about how VBDs and Virtual Disks are (currently) 
implemented, some info about the tools and a little walkthrough of an example 
task.  The VBD / VD functionality is a bit like LVM and works in a similar way.

The current state of play is this:
* virtual disks are allocated from a pool of space set aside in one or more 
whole partitions or disks.  They can't, for instance, just be files on some 
other domain's filesystem.
* virtual disks can be created from that pool of free space as needed.  Space 
reserved for a particular virtual disk is then allocated and hence unusable 
for other virtual disks, even if untouched by the domain it belongs to.  This 
guarantees that space will be available if / when needed by the domain.  As a 
result you can't speculatively "overbook" your virtual disk free pool.
* You can enlarge existing virtual disks, export them to files, import from 
files and various other useful things (details in the readme / howto).
* You can add and remove VBD access to / from domains dynamically, rather like 
hot plugging (e.g. to access a filesystem from dom0).

Like Ian said, make sure you don't have filesystems writeable by more than one 
domain at once - most filesystems can't cope (and will get very badly 
corrupted).  (actually, Linux also gets confused if someone else is writing a 
filesystem it has mounted read only but this shouldn't cause corruption).  
There's some sanity checking for shared disk mappings in the tools.

Some of the VBD / VD stuff might change in the new I/O world.

HTH.

Mark



-------------------------------------------------------
This SF.Net email is sponsored by: IBM Linux Tutorials
Free Linux tutorial presented by Daniel Robbins, President and CEO of
GenToo technologies. Learn everything from fundamentals to system
administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel