infrequently used filesystem gets VERY slow

[Gore Jarold]

Two machines, almost identical (same 3ware 9650se sata raid card, same 500 GB hitachi drives, etc.)

First machine is running 6.1-RELEASE ... never noticed anything odd.

Second machine is running 6.2-RELEASE.

These machines are very simple office fileservers.  So there is a / partition, a /var, and then a big monster raid-5 array with all the rest of the space.  So it is very rare that anyone actually runs any interactive commands in the shell or does any access to files on the / or the /var filesystems.  The VAST majority of all usage is on the big array.

On the first machine (6.1) there is no noticable lag when accessing / and /var ... 
but on the second machine (6.2) there is a very long wait - sometimes 20 seconds or more - for commands that deal with the / or /var ... for instance, if I:

grep username /etc/passwd

or:

tail -200 /var/log/messages

those commands can take 10-20 seconds to complete.  But then, if you run subsequent commands they are quick.  Once you do some work on / or /var, their speed picks back up.

So it would appear that files in / and /var are just nowhere in the cache at all ... which isn't so odd, but what is odd is that the problem is not seen on the first system.

So was there any major differences between 6.1 and 6.2 in the filesystem caching and strategies that would account for this difference ?  Any comments at all on what I am seeing ?

       
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