An olpcfs experience report
Joshua N Pritikin
jpritikin at pobox.com
Fri Apr 25 12:30:14 EDT 2008
On Fri, Apr 25, 2008 at 12:12:28PM -0400, C. Scott Ananian wrote:
> In the current olpcfs1 implementation, all metadata is stored in
> Berkeley DB; the actual file contents are stored in a simple
> content-addressable store.
You say "content-addressable store," but what does that mean
implementation-wise? Does that mean that OLPCFS hashes the content of
the file into a metadata tag when the file is closed?
In particular, I am wondering what happens when I save a movie made with
Record (i.e. save a big file). How much additional overhead does OLPCFS
I presume that the file is not copied an additional time. However, does
OLPCFS need to read the file again to calculate the hash? If it does,
can it (eventually in version 2) do this in the background?
> If you use BDB correctly, it seems to me to be pretty solid and mature
> -- a conclusion which concurs with the long list of BDB users.
Sure, but BDB would be even more trustworthy if I could 'rm -rf' the
database and regenerate it from scratch without losing data. If metadata
was stored in POSIX xattrs then it would seem like your design permits
this mode of operation.
I have seen enough instances of "foolproof" databases that I think we
should minimize reliance on them.
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