[OpenAFS] [Q] Funny Traffic ...

Thu, 27 Mar 2003 12:21:55 -0700

Hello again,

You'll want to look at the value "cacheBlocksInUse" and the value
"cacheBlocksTotal."

Set the refresh time for afsmonitor to 3 seconds or so.

When the cache appears to be almost full (cacheBlocksInUse approaches
cacheBlocksTotal), the number of dcache items in use
will begin to drop -- meaning that the cache manager is beginning to free up
some cache space.

It's at this point I experienced the "hesitation," with very large caches
and very small data files (not quite the same setup as yours).

You're also interested in "cacheCurrDirtyChunks."  Before dirty chunks are
garbage collected, they have to be pushed back to the fileserver.  It would
take a lot of dirty chunks to affect garbage-collection time (they're
ignored when cache space is reclaimed, unless there are so many that they
_must_ be freed up), but it shouldn't be overlooked.

If you don't see this behavior (cacheBlocksInUse approaches
cacheBlocksTotal, and then reduction in cacheBlocksInUse) let me know.
There are other things that will trigger cache purges -- like running out of
Vfiles -- that will cause a cache purge to take place even though you've got
lots of cache (disk) space left.

WRT to chunk size, a client was looking for performance improvements and
experimented with 1 MB chunk size.  In their environment (AFS on a Cray,
CDDI to every user's desktop, several hundred megabyte data files) they saw
no improvement over the 64K default. Then again, they had a lot of hardware
horsepower at the time, had the Cray set up to run multiple instances of the
OS, and ran AFS server software for each instance of the OS.

According to the IBM AFS Administration Guide for AFS 3.6, setting
the -chunksize argument to 0 or setting it to anything greater than 30 will
cause afsd to set default chunksize.

In other words, valid values are 1-30, unless you want to reset to the
default of 64K.

Chunk size is set as 2 to the power of -chunksize.  That is, if you specify
"-chunksize 2" you'll get a chunksize of 4 bytes, and "-chunksize 16" will
get you a 64 K chunk size, which is the default.

2E30 or 1.073741824e9  (a gigabyte) is the largest chunk size permitted by
IBM/Transarc AFS 3.6.

So "-chunksize 30" should give a one gigabyte chunk size.

And "-chunksize 21" will give you a 2MB chunk size.

"-chunksize 20" will give you a 1 MB chunk size

and your chunksize value, to get the 256K chunks, must be 18, right?

Probably more than you wanted/needed to know.

Let me know what works in your circumstances, please.  I run into this
question frequently, and am way out of date on results.

It's been several years since I fooled around with any of this, and current
hardware speeds may invalidate what I found then.

Kim

---------------------------------------------------
Dexter "Kim" Kimball
CCRE, Inc.
dhk@ccre.com
P970.207.1525
C970.215.6359
F970.207.1474
---------------------------------------------------

----- Original Message -----
From: "Sungjin Chun" <chunsj@workspace.buchun.thrunet.com>
To: "Dexter Kim Kimball" <dhk@ccre.com>
Cc: <openafs-info@openafs.org>
Sent: Wednesday, March 26, 2003 7:11 AM
Subject: Re: [OpenAFS] [Q] Funny Traffic ...

> Thanks for your help, here comes another question :-)
>
> How can I know that the "hesitation" occurs using afsmonitor, what value
> should I consult? And current chunksize is 256K, if bugger one shows
better
> performance, what is the limit ofr chunksize?
>
> Thanks in advance.
>
> On Tue, Mar 25, 2003 at 08:31:44AM -0700, Dexter Kim Kimball wrote:
> > Use afsmonitor to look at your cache behavior.
> >
> > You may find that the "hesitations" occur when the cache is purging.
> >
> > If so, reduce cache size and repeat benchmarking until the hesitations
go
> > away.
> >
> > With the large files you describe, I'd also look at changing the default
> > chunksize (look at arguments to "afsd") from 64K to something much
larger.
> >
> > Kim
> > ---------------------------------------------------
> > Dexter "Kim" Kimball
> > CCRE, Inc.
> > dhk@ccre.com
> >
> >
> > ----- Original Message -----
> > From: "S.J.Chun" <chunsj@embian.com>
> > To: <openafs-info@openafs.org>
> > Sent: Tuesday, March 25, 2003 8:18 AM
> > Subject: [OpenAFS] [Q] Funny Traffic ...
> >
> >
> > > Hi,
> > >
> > > We are using one OpenAFS server and one OpenAFS client, through the
client
> > we are serving files(
> > > rather big sized files, normally 600~800MB) using apache http server.
Now,
> > we have BIG performance
> > > problem. We've chosen AFS for its high scalability but the performance
is
> > very bad. We are using
> > > 100M dedicated line and expected the download speed as up to 800K or
> > 1,000K through our cable
> > > or ADSL line, but only got 40 ~ 80K. What is the best configuration
for
> > our purpose?
> > >
> > > And if I try to get file using ftp, the data transfer is rather funny;
it
> > gets 256K of data, then waits some
> > > times(several seconds) then again gets another 256K of data. Why the
data
> > transfer is not continuous?
> > > Misconfiguration?
> > >
> > > The server has 2 TB of storage and the client has 9GB of cache. And OS
is
> > Linux.
> > >
> > > Thanks in advance.
> > > _______________________________________________
> > > OpenAFS-info mailing list
> > > OpenAFS-info@openafs.org
> > > https://lists.openafs.org/mailman/listinfo/openafs-info
> >
> > ----- Original Message -----
> > From: "S.J.Chun" <chunsj@embian.com>
> > To: <openafs-info@openafs.org>
> > Sent: Tuesday, March 25, 2003 8:18 AM
> > Subject: [OpenAFS] [Q] Funny Traffic ...
> >
> >
> > > Hi,
> > >
> > > We are using one OpenAFS server and one OpenAFS client, through the
client
> > we are serving files(
> > > rather big sized files, normally 600~800MB) using apache http server.
Now,
> > we have BIG performance
> > > problem. We've chosen AFS for its high scalability but the performance
is
> > very bad. We are using
> > > 100M dedicated line and expected the download speed as up to 800K or
> > 1,000K through our cable
> > > or ADSL line, but only got 40 ~ 80K. What is the best configuration
for
> > our purpose?
> > >
> > > And if I try to get file using ftp, the data transfer is rather funny;
it
> > gets 256K of data, then waits some
> > > times(several seconds) then again gets another 256K of data. Why the
data
> > transfer is not continuous?
> > > Misconfiguration?
> > >
> > > The server has 2 TB of storage and the client has 9GB of cache. And OS
is
> > Linux.
> > >
> > > Thanks in advance.
> > > _______________________________________________
> > > OpenAFS-info mailing list
> > > OpenAFS-info@openafs.org
> > > https://lists.openafs.org/mailman/listinfo/openafs-info
> >