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

[Riaan van Niekerk]

Robert Peterson wrote:
> 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 are no longer applicable due to design changes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.
> 
> Regards,
> 
> Bob Peterson
> Red Hat Cluster Suite
> 
hi Bob

I find it extremely unfortunate that you felt it necessary to remove 
this article. From Wendy's reply I can deduce that most of those issues 
still persist, meaning that with regards to NFS on GFS at least, the 
document is still very relevant.

I know you guys are pretty busy, and I sincerely hope that you or 
someone will get/make the time to write an architectural overview and 
detail document of GFS, perhaps even use Ken's original document as a 
base. I will gladly provide feedback on such a document, once you have 
written it.

(Aside: asking a user looking for info on the innards of GFS (and this 
has been asked before on the list) to settle for a cookbook on NFS on 
GFS is just a long shot - with all respect).

My biggest regret is to not have saved a copy of this document locally. 
  It really contained quite a bit of useful information in my mind, 
despite it being old and in parts deprecated.

all the best
Riaan
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