[OpenAFS] Re: why afs backup is so poorly supported
Thu, 12 Oct 2006 08:58:14 -0400
On Oct 10, 2006, at 5:24 PM, Matt Benjamin wrote:
> Cool as the transactional piece would be, iirc from our discussion
> in 2004, putting a postgresql behind every fileserver sounds kind
> of heavyweight, doesn't it?
> Plus, is there a difference between transactional metadata updates
> and transactional file data updates?
There have been various claims about the overhead of using a dbms as
a file server. There's an excellent paper out there somewhere
(translation: I'm too damned lazy to look for it (again)) on the
Inversions file system, a project which built a fs on top of
University Ingres. It was presented at a USENIX. As I recall, they
claimed somewhere about a 2:1 overhead in general.
With respect to the metadata differences, yeah, they're huge. Most of
what a file system would call metadata is just another entry in a
table. Those tables themselves have metadata, but if an entire fs
worth of metadata were contained in a single table, the transactional
costs would be hugely smaller (in my humble and only semi-educated
opinion, of course).