[Lustre-devel] Replication

[Nikita Danilov]

Peter Braam writes:
 > On 5/6/08 11:43 AM, "Nathaniel Rutman" <Nathan.Rutman at Sun.COM> wrote:

[...]

 > > 
 > > For 2 and 3, we could store the directory name for each directory in an
 > > EA, and all the fids for all the parents in some other manner.
 > > But it seems to make more sense at this point to put all this
 > > information (fid, name, parent list) in a database file stored on the
 > > MDT.  Then we just look through this database to generate our full path

One advantage EA has over global data-base is that the former is more
resilient against file system corruption. This becomes more important if
we ever plan to use (parent-fid, name) information for things like fsck.

 > > information; no need to lookup info in the file objects or EAs.
 > > Generating this database should be no more time consuming than writing
 > > the changelogs themselves, assuming a reasonable database structure like
 > > IAM.

On a lower level note, I think that changelogs and parent-database are
better to be implemented as a new layer separate from mdd:

    - mdd code is already complicated enough,

    - separate layer can be inserted into stack optionally, avoiding
    run-time cost if change-logs are not needed (currently there is no
    way to insert a layer after initial configuration completes though).

 > > 
 > 
 > Yes I agree with all of this.
 > 
 > Peter
 > 

Nikita.