Re: [Evms-announce] EVMS announcement

Mike Diehl
2002-11-05T23:34:53Z

Well, I'm a bit disapointed. My experience with LVM has been nothing
short of disasterous; EVMS looked like a very good alternative to LVM.
Volume Management is one of the FEW things that Linux lacks that the
"Big Boys" have.

<pause> I got up to get a drink and my 2-year-old jumped up to my desk and
sent this... Continue Ranting....

The biggest thing that EVMS had going for it was it's modular design. As I
understand it, EVMS could even be used to manage the current MD and LVM
drivers. I was looking forward to partition-level encryption, etc.

I wish the decision had gone the other way. Get rid of LVM and get EVMS into
the mainstream. Any chance that, after this "migration," we might do just
that? I'd love to see the day when LVM and MD aren't kernel options by
themselves, but rather options under EVMS, along with lots of other cools
things.

But never mind me. I'm just a linux user, not a linux developer.

> On Tuesday 05 November 2002 05:19 pm, Kevin Corry wrote:
> > Greetings EVMS users,
> >
> > On behalf of the EVMS team, we would like to announce a
> > significant change in direction for the Enterprise Volume
> > Management System project.
> >
> > As many of you may know by now, the 2.5 kernel feature freeze
> > has come and gone, and it seems clear that the EVMS kernel
> > driver is not going to be included. With this in mind, we have
> > decided to rework the EVMS user-space administration tools (the
> > Engine) to work with existing drivers currently in the kernel,
> > including (but not necessarily limited to) device mapper and
> > MD.
> >
> > Why make this change? With EVMS being passed over for inclusion
> > in 2.5, the future of the EVMS kernel driver becomes very
> > uncertain. We could obviously continue working on it and keep
> > it up-to-date as a patch against the latest kernels. Numerous
> > helpful comments and changes were suggested during the review
> > of the code last month on the kernel mailing list. We could
> > spend the time to make many of the desired fixes, including
> > some architectural and interface changes. However, the one
> > issue that has not been addressed at length is EVMS's in-kernel
> > volume discovery mechanism. We believe that even if the other
> > changes are made, this will eventually become an issue at a
> > later time. Moving discovery to user-space is certainly a
> > possibility. However, at that point, it would become difficult
> > to differentiate the EVMS driver from the device mapper driver,
> > since they would be performing very similar tasks.
> >
> > In addition, there would be no need to maintain duplicate MD
> > kernel code in order to provide compatibility with existing
> > software RAID devices. Obviously this duplication has been a
> > significant issue, but it was an unfortunate necessity in order
> > for MD devices to be discovered within the current EVMS kernel
> > framework. With discovery moving to user-space, the EVMS tools
> > can simply be rewritten to communicate with the existing MD
> > driver in the kernel. This approach allows MD to be used
> > directly, without requiring it to be immediately ported to
> > device mapper. However, if the decision is made in the future
> > to make that port, then the EVMS tools should only become
> > simpler.
> >
> > We will also emphasize that this change has not been made
> > suddenly or without a great deal of thought. We have been
> > contemplating this possibility since shortly after the Ottawa
> > Linux Symposium in July. However, we continued to develop the
> > EVMS kernel driver because of input from our users. We wanted
> > to go ahead and submit the driver and get the opinion of the
> > full community before making this decision. In the last few
> > weeks it has become clear that the current EVMS approach is not
> > what the kernel community was looking for, so we have spent
> > that time determining the feasibility and consequences of
> > making this switch. We have come up with a good initial plan,
> > and everyone involved now agrees that this is the best course
> > of action.
> >
> > So how will this switch affect the EVMS users? Ideally, we want
> > the users' experience with EVMS to remain completely unchanged.
> > Based on our current plans, the user interfaces will not have
> > to change at all, since we don't see any major changes to the
> > Engine's external application interface. The plan is to provide
> > the same, single, coherent method for performing all volume
> > management tasks. This change will be almost transparent for
> > most users. The same features, plugins, and capabilities will
> > be supported.
> >
> > There will, of course, be some minor changes. Specifically,
> > installing EVMS will be slightly different. It will involve
> > different kernel options than you are used to with the current
> > version. In the 2.5 kernel, all of the major components are
> > already present, so little, if any, kernel patching should be
> > necessary. Since device mapper has not yet been included in the
> > main 2.4 kernel, 2.4 users will still require kernel patches.
> > In addition, some functionality still does not exist in any of
> > the available drivers. Specifically, we may provide extra
> > device mapper modules for features like bad block relocation.
> > The installation of the EVMS engine tools, on the other hand,
> > should not change significantly from the current method.
> >
> > The other major difference will be due to the move to
> > user-space discovery. First of all, why make this switch? The
> > most obvious reason is that the kernel drivers become much
> > simpler, and the only things they need to provide is I/O
> > handling and a method for activating the volumes. While disk
> > partitioning and software RAID still perform discovery in the
> > kernel, the trend seems to be to move these tasks to
> > user-space. It is likely at some point in the future that
> > partitioning and MD will also be moved out of the kernel as
> > well. However, the drawback to making this switch is losing
> > automatic boot-time volume discovery. Activating EVMS volumes
> > will now require a call to a user-space utility, which will
> > need to be added to the system's init scripts in order to
> > activate the volumes on each boot.
> >
> > In addition, this switch complicates having the root filesystem
> > on an EVMS volume. Currently there is a lot of work being done
> > on adding initramfs to the 2.5 kernel, which will provide a
> > pre-root-fs user-space. This new system should provide a simple
> > method for adding tasks to run during this early user-space,
> > and those who wish to use root-on-EVMS will just need to add
> > the EVMS tools to their initramfs. For 2.4 users, this means
> > using an initial ramdisk (initrd) to provide this same pre-root
> > user-space. Initrd setup is certainly awkward and often
> > distribution- specific. But we will do our best to provide
> > adequate instructions and assistance to those who need help in
> > that situation.
> >
> > Looking ahead, we *will* continue to *fully* support the 1.2.0
> > version of EVMS on 2.4 kernels, and possibly release a 1.2.1
> > version with some recent bug fixes. We will also make a
> > reasonable effort to maintain the current EVMS kernel driver on
> > 2.5. It will not go through any other major changes, but we
> > will try to keep it up-to-date and working with the latest 2.5
> > releases, until the new EVMS tools are complete. At that point,
> > the 2.5 EVMS driver will be dropped. Also, the new enhancements
> > we have been working on recently, such as clustering and volume
> > move, will only be developed under the new Engine model, and
> > will not be available for the current 1.2.x code base.
> >
> > So how long will this take? Currently, we are estimating that
> > we can have the user-space volume activation framework working,
> > along with initial support for most of the plugins, by early
> > 2003. Certain features, such as BBR and Snapshotting, may take
> > longer to work out the details of their operation. We will soon
> > open a new CVS tree to hold the new Engine code, leaving the
> > old trees as a repository for bug fixes to the 1.2.x version.
> >
> > In summary, we feel that this decision is the best way to
> > support our users for the long term. We want to provide EVMS on
> > current and future kernels, and we feel this change provides
> > the best method for achieving that. At the same time, this
> > addresses all of the concerns voiced by the kernel community.
> > If anyone has any questions or concerns about this decision,
> > please email us or the EVMS mailing list at
> > evms-devel@lists.sf.net. We will be happy to answer any
> > questions or discuss these changes in more detail.
> >
> > Thank you,
> >
> > The EVMS Team
> > http://evms.sourceforge.net/
> > evms-devel@lists.sourceforge.net
> >
> >
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Mike Diehl
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