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
>softupdates
> 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
servers.
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
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