[Libvir] Re: parted/LVM for ET [Storage manager initial requirements and thoughts

Daniel P. Berrange berrange at redhat.com
Thu Jun 14 15:01:33 UTC 2007

On Thu, Jun 14, 2007 at 03:50:28PM +0100, Richard W.M. Jones wrote:
> Jim Meyering wrote:
> [...]
> Thanks for looking into this.
> >In addition, there is the fact that Parted's partition-table (aka
> >what it calls "label") support is currently tied to a 512-byte sector
> >size for many label types.  BTW, do any of you know which are the
> >partition types that matter the most to us?  MSDOS and GPT seem like
> >the top priority ones, and I've fixed most parts of those two, but
> >have only lightly tested the GPT changes.  Also, with >512-byte sector
> >devices becoming more and more common (e.g., ipods, CDs, new-and-bigger
> >disks), I wonder how important it is to make Parted work for them, now.
> >Fixing Parted for the few most common partition types isn't a big deal,
> >but fixing all of them would require more time and testing resources than
> >I expect to have.  I plan to leave most of the others in their current,
> >works-only-for-512-byte-sectors state.
> From the virt-manager/libvirt p.o.v. it seems to me the important 
> operations are:
> (1) Find attached drives.
> (2) Find partitions available & their sizes.
> (3) Allocate logical volumes.
> (4) Find out how much free space is available on a partition, and carve 
> out a file.
> Correct me if I'm wrong (I usually am), but:
> Nothing can do (1) except doing a brute force scan over /dev and looking 
> for likely block devices (this is what vgscan does).

HAL can do this for physical devices.

> Parted can do (2), with several limitations including sector size.  It 
> can't do (3) at all, but then neither can anything else except forking 
> the LVM command line tools.
> And (4) can be done by libvirtd using ordinary POSIX calls, so no 
> external library support is needed, just some work to remote those 
> operations (which is mostly done).

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