As mentioned here (ibm) and in this thread, there is no direct tool to import SVN data to ClearCase.
That means a custom script setting your SVN workspace to relevant milestone, and then clearfsimport those into a ClearCase view with a "proper" config spec (i.e. "configuration specification").
By proper, I mean a ClearCase view importing into the relevant ClearCase branch the different copies of Subversion files located into 'branch directories'. And then importing in the right order the 'tags' (still copies in the SVN repo) in the ClearCase import view, with a label set right after that kind of import.
So the main 'gotcha' is to blindly import the all SVN structure: that would result in actual directories which should not be present at all in ClearCase, since branches and tags are first-class citizen with this tool, and not 'cheap copy' like in SVN.
A good script to start with (and to adapt of course) would be svn2git which does detect SVN branches and tag, and try to import the content of those 'directories' into git, (but could also import them into ClearCase, through the right system call to the 'clearfsimport' command').
Since the import of a single revision can be fairly long, a realistic approach would be to limit the script to only import:
- tags
- HEAD of trunk
- HEAD of the declared branches
When importing branches, that means creating the brtype, and then setting a label (a starting point), finally changing the config spec in order to get the following selection rules:
element * .../svnBranch
element * STARTING_LABEL -mkbranch svnBranch
element /main/0 -mkbranch svnBranch
The important point is to have an end result without the directories representing branch and tag present in SVN.
From there, you will be able to move/rename the main directories into whatever structure you want, like the one suited for UCM component declaration (if you want to use UCM).
I can't speak for the migration tool, but mercurial has worked great for us. We have a mix of WinXP, Mac OS X, and Linux people and there haven't been any snags. I don't use an IDE, but I believe Aptana acquired the pydev group (Python for Eclipse) so I wouldn't be too surprised if they have that.
Best Answer
For having made several migrations of this kind, I would argue that:
you do not need to import all the history of the ClearCase versions into SVN. Most of the time (for my experience), only the labeled versions (the one which are applied consistently on all the files of a given set) are needed, unless you have a real need for a fine-grained history revision examen.
you need to think about reorganization during a migration: what do you import ?, what do you leave ?, and do you want the SVN content reflect exactly the structure of the files as stored in the ClearCase VOB ? Sometime, such migrations are the occasion to rethink some of those files organization (usually through simple renaming rules for certain directories).
the migration is quicker in the ClearCase 2 SVN way, since SVN is repository-centric and commit a set of files, while ClearCase is file-centric and commits file-by-file (much sloooower)
if the set of files to import is clearly identified, the migration process can be repeated multiple times over, which means you can go on working within ClearCase while the first (large) import is taking place, then put a Baseline (UCM label) on your code, and re-import only the delta, effectively ending the migration process.