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Re: [Linux-cluster] gfs2 v. zfs?



On Tue, Jan 25, 2011 at 11:34 AM, yvette hirth <yvette dbtgroup com> wrote:
> Rafa Grimán wrote:
>
>> Yes that is true. It's a bit blurry because some file systems have
>> features others have so "classifying" them is quite difficult.
>
> i'm amazed at the conversation that has taken place by me simply asking a
> question.
>
> *Thank You* all for all of this info!

We purposely diverted your question to backup, since it is easier to
have productive discussions (compared to directory list) :) ... In
general, any "walk" operation on GFS2 can become a pain for various
reasons. Directory listing is certainly one of them. It is an age old
problem. Other than the inherited issues from the horrible stat()
system call, it is also to do with the way GFS(1/2) likes to
"distribute" its block all over the device upon write contention. I
don't see how GFS2 can alleviate this pain w/out doing some sorts of
block reallocation.

I'll let other capable people to have another round of fun discussions
.... Maybe some creative ideas can get popped out as the result ...

-- Wendy

>
> we've traced the response time slowdown to "number of subdirectories that
> need to be listed when their parent directory is enumerated".
>
> btw, my usage of "enumeration" means, "list contents".  sorry for any
> confusion.
>
> we've noticed that if we do:
>
> ls -lhad /foo
> ls -lhad /foo/stuff
> ls -lhad /foo/stuff/moreStuff
>
> response time is good, because , but
>
> ls -lhad /foo/stuff/moreStuff/*
>
> is where response time increases by a magnitude, because moreStuff has ~260
> directories.  enumerating moreStuff and other "directories with many
> subdirectories" appear to be the culprits.
>
> for now, we'll be moving directories around, trying to reduce the number of
> nested levels, and number of elements in each level.
>
> in human interaction there is a rule:  as the number of people interacting
> increases linearly, the number of interactions between the people increases
> exponentially.  is it true that as the number of nodes, "n", increases
> linearly, the amount of metadata being passed around / inspected during disk
> access increases geometrically?  does this "rule" apply?  or does metadata
> processing increase linearly as well, because the querying is all done by
> one node?
>
> thanks again - what a group!
> yvette
>
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