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Re: [Linux-cluster] NFS on GFS architectural issues / problems

Riaan van Niekerk wrote:
hi Bob and others

I found on the Red Hat 108 Developer Portal the following GFS1/GFS2 design document which details amongst others, some of the issues with NFS on GFS: https://rpeterso.108.redhat.com/servlets/ProjectDocumentView?documentID=99

(I see it was sent to this list over a year ago, but I never found it while searching through the archives. it has a lot of good information in it)

It has a disclaimer: Some of the comments
are no longer applicable due to design changes

My question to you or anyone who is familiar with NFS on GFS, or GFS in general, which of the following are still valid issues for the current (6.1u4) version of GFS. If all or most of them still apply, I can use this as motivation for my customer to strongly consider going off NFS on GFS. Removing the NFS from our GFS cluster has been on the cards for quite a while, but has not gained momentum due to lack of information on the performance gains of such a move (very difficult to gage) or the architectural problems/limitations of NFS on GFS (for which the following extract is spot-on).

Note - can you consider adding a link to this document from your FAQ?
Hi Riaan,

The document you mentioned was written by Ken Preslan more than a year ago.
It has some good architectural information regarding GFS and GFS2, but the problem is, there have been a lot of changes to GFS2 and a lot of work has been done on NFS since that time,
so a lot of it no longer applies.

One day I was playing with 108 and decided to upload the document to my 108 page because I thought it was "a good find" and there was a need for GFS architectural information on the Internet. Afterward, I was discussing the article with some of the developers and they all agreed that the article shouldn't be posted because it contained too much misinformation due to recent changes made to all areas of the code. The problem is, I had already posted the article and I couldn't figure out how to get 108 to delete it. (Today I figured out how to delete it, and did so, and I apologize if anyone was misled by what it says. I'm going to file a usability bugzilla against 108 though.)

What I really need to do is write a white paper about GFS and its internals and its structures, rather than spending the time required to sift through Ken's article and separate fact from "no longer applicable". And the link to that document will certainly be added to the FAQ.

There are some known issues with NFS failover, but it works great unless you're intentionally trying to break it by doing some nasty tricks such as those documented in bugzilla 178057. If you read the first few comments of the bugzilla, you'll see that I tried very hard at first to break it and couldn't. Wendy Cheng has been spearheading the effort to improve NFS failover and I applaud her efforts.


Bob Peterson
Red Hat Cluster Suite

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