Cluster Computing and MapReduce Lecture 3

At the beginning of the lecture, he says that NFS is a POSIX file system. It isn't. I'm sure he just misspoke and meant to say that it's a networked file system popularly used with POSIX operating systems.

NFS is a POSIX-*compliant file system*.

Thanks for the clarifying his exact words.

However, NFS isn't POSIX *compliant* either. Open Group's XNFS specs explain how NFS semantics differs from POSIX/SUS in over 10 pages of detail.

good.
how gfs helps MapReduce

In the latter part of the presentation, there is talk and notes about file deletion. It was said that the file that is to be deleted is given a hidden name and then at a later time when the Master Server is slow, Then it can then delete these hidden files.

This does not make sense to do a seperate operation to delete files for the hidden file names will simply be written on when the controller need the space of the drive.

In the paper, it is described that if the user retries to delete a file, then it is immediately deleted. The gfsutil actually has different parameters to force delete a file immediately in order to reclaim space immediately.