Why WAFL is Not a File System.

In response to a set of comments, I wrote up a series on WAFL to address the common misconception about WAFL being a file system and in particular, how SAN is layered within Data ONTAP.

This post will act as a launch point to that series.

In my first post, I explained why the notion that WAFL is a file system did not match my experiences using WAFL.

Next I explored what is a file system and offered a reasonable set of attributes that defined a file system.

Then I compared WAFL to those attributes. I used that comparison to argue WAFL was not a file system but something new.

I then turned to the question of how WAFL and SAN are layered.

Finally I offered some thoughts on why there is so much confusion about WAFL.

Comments

[Steven Schwartz - The SAN Technologist]

Thank you for the in depth write up over the past several days.

I wasn't trying to be difficult, just trying to better understand how NetApp was handling Unified Storage, since it appears that different people within NetApp have explained it in different ways. It is also clear that WAFL has changed over the years from it's original design.

My first feeling on why I had considered it a "file system" was based on how it talked about, and the recent legal "conversations" about WAFL and ZFS.

I look forward to diving deeper into your posts over the next few days so I can get a better handle on NetApp's WALF in this millennium.

[Martin G]

Can I add to Steven's thanks; it's been a very interesting read. I'm going to have to a good read and think.

To a certain degree, I wonder if it all really matters; if it works and you get the performance/features that us users require, who cares if you are storing your data in cardboard boxes in a storage facility in Outer Mongolia?

Technically, it's interesting and I like to know what's going on under the covers but ultimately, it shouldn't matter! All vendors like to throw FUD around, some more openly than others. It's up to the informed user to question the FUD.

[kostadis roussos]

Martin,

First off, thanks for the kind words.

I think you thumped the proverbial nail with the proverbial hammer.

How WAFL is, is interesting if you are an engineer, irrelevant if you are customer.

Ultimately NetApp storage systems should be judged on their ability to meet customer requirements, not on how they may or may not be architected.

If you want a longer set of posts on this idea, you can check out:

http://blogs.netapp.com/extensible_netapp/group_theory/index.html

cheers,
kostadis

[kostadis roussos]

Steven,

I hope I clarified my statements about WAFL.

Of course, I must admit the whole WAFL is a Platypus post makes me wonder if I clarified anything.

cheers,
kostadis

[kostadis roussos]

Martin,

Dang, your platypus post cracked me up.

As to why bother writing all of that text? Like you said, it should be irrelevant to our customers...

So why did I write it up?

Because our competitors insist on making factually incorrect statements about our technology.

For some of our competitors it's just plain ignorance. Since we've done so much to not share with folks the layering, I can only blame NetApp.

But there are EMC employees, like the Oracle Storage Guy, who abuse their prior relationship to NetApp, abuse the lack of information on the net, to wilfully spread misinformation about the relationship between SAN and WAFL.

So this is about providing some facts to counter some of the distortion.

cheers,
kostadis

[Martin G]

It's a great thing to write it up; it was something which needed to be done. It would be nice if it was turned into a white-paper BTW. It's not necessary for me to understand how my storage arrays work but it is useful.

And I'm glad you liked the Platypus thing.