At 9:34 AM -0700 2000/4/27, Matthew Dillon wrote:

>      I can't imagine why MFS would perform better... it shouldn't, every
>      block is stored in system memory *TWICE* (once in the VM cache, and
>      once in the mfs process's address space).  If you have enough system
>      memory to create a large MFS filesystem and it performs well, then
>      the system should perform even better if you remove the MFS filesystem
>      and just use a normal filesystem.

        When I tried using a regular file on the filesystem, my system 
time went way up, my iowait went way up, and my performance dropped 
through the floor.  However, this was on 3.2-RELEASE and was several 
months ago -- I hope that 4.0-STABLE would be a bit better about 
that.  ;-)

>      I would consider trying a normal filesystem with an async or a 
>      mount.  Or a normal filesystem with softupdates enabled.  It may also
>      help to turn off write-behind (sysctl -w vfs.write_behind=0), though if
>      you are running the latest 4.x stable the write heuristic is now in and
>      should do a good job on its own.

        I believe I had tried this with softupdates at the time, but it's 
been long enough since I tried this that I can't be sure.  I do 
recall seeing my performance go down quickly enough and seeing the 
disk I/O go through the roof fast enough that I decided I would 
never, ever, ever try that again.  Of course, now I am revisiting 
that decision.  ;-)

        I'm seriously contemplating getting a Dell PowerEdge 2450 with 
five internal 10kRPM/18GB disks, 2GB of RAM, two of the fastest 
processors they've got, perhaps a pair of Intel EtherExpress Pro 100+ 
NICs, and giving this another go with FreeBSD 4.0-STABLE.

        Do you have any thoughts on this subject?  Is 3.2-RELEASE old and 
non-optimized enough that it really could stand replacing?

        Given some of the problems we've been seeing lately (which I'm 
pretty sure are a result of running out of virtual memory and the 
machine spontaneously rebooting), I think I might be able to convince 
my management to spring for a third 2450, but with a slightly 
different configuration than what I'll be using for the news reader 

        It would help me formulate useful arguments for this proposal if 
I had input from more knowledgeable people than I.

   These are my opinions -- not to be taken as official Skynet policy
Brad Knowles, <[EMAIL PROTECTED]>                || Belgacom Skynet SA/NV
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Phone/Fax: +32-2-706.13.11/12.49             || B-1140 Brussels                         || Belgium

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