[1079] in linux-scsi channel archive
Re: news on dual buslogics with MD
daemon@ATHENA.MIT.EDU (Alan Brown)
Sat Dec 7 03:16:54 1996
To: submit-linux-dev-scsi@ratatosk.yggdrasil.com
From: alan@papaioea.manawatu.gen.nz (Alan Brown)
Date: 7 Dec 1996 20:50:07 +1300
In article <199612030624.WAA00624@dandelion.com>,
Leonard N. Zubkoff <lnz@dandelion.com> wrote:
>First, why a dual processor machine? As far as I'm aware, news is generally
>I/O bound rather than CPU bound, so I don't see what the extra processor is
>buying you. Also, Linux' SMP support is best at compute bound tasks since only
>one processor can be in the kernel at a time. Given the high I/O load on a
>news server, I'd suggest you get a single P6-200 rather than a dual P5-200.
>Make sure you have enough memory that the machine never pages.
I'd encourage putting in as much ram as possible, but here's my
experience from running a news server for the last 5 years....
99% of the time the machine is i/o bound, however when you have a lot of
outgoing channel feeds or 10,000+ newsgroups, whenever a newsfeed is
altered or a newsgroup added/removed, you go into a situation where the
machine does a LOT of numbercrunching for a short space of time as the
entire active file + newsfeeds file is held in memory in a database
format and must be updated.
Additionally, whenever a change is made, all the channel feeds are
terminated and respawned. This eats a lot of cpu - my current 486dx2/66
is well behind the curve in this dept and it causes a 2-4 minute pause
each time there's a change. As I allow all my feeds to alter their
newsfeeds automatically via gup, there're always changes going on, plus
there's the constant trickle of group control messages.
Currently I have 200 uucp feeds done through a funnel and 28 channel
feeds feeding into nntplink. I'll be changing this to innfeed as it'll
allow me to turn the channel feeds all into funnel feeds and get round
the high drop/spawn overheads associated with each one while still being
able to do "instant feeding" plus using innxmit to stream anything which
has been dropped (such as when the remote has throttled thru lack of space).
Given a choice between running 256Mb of ram and a dual processor machine
I'd take the ram every time however. :-)
For expandability, I'd recommend the following:
1: Use a motherboard capable of taking at least 512Mb ram. It sounds
ridiculous today, but so did needing 128Mb 2 years ago. If you can
find a 1024Mb capable machine, so much the better.
2: Consider fibre channel and a scsi frame capable of hot swapping.
The big question is whether any fibre channel controllers are readily
available yet and what the availability of Linux drivers is like.
3: Make your building block either 4Gb or 9Gb drives, but ensure you start
with at least 4 on the news spoool and that they're 7200rpm ones with
lots of cache. The more spindles the better.
4: System binaries, swap, news binaries, news library files, news logs,
news spool and overview should all be preferably on separate spindles
or MD blocks if they're big enough to warrant being on multiple drives
apiece. It's expensive, but it all helps reduce the waiting on i/o. :-)
Using multiple scsi busses goes without saying. Even with Fibre channel
it's quite easy to max a bus of you have too many drives on it.
5: Be prepared to see whatever you use become worth next to nothing in
less than 2 years. We spent $22,000 on our news server and it needs
replacement already.
6: Related to 5, make sure that whatever you get is expandable. We got
caught out on the hardware we bought, as I'd specified things to allow
for upgrading, but the actual specs of the platform we bought were a bit
different from what the NZ agents claimed they were (Acer Altos 700i
server), so it's actually going to be cheaper for us to scrap it and
start over. NZ depreciation laws allow us to completely write the machine
off at 36 months, so there's a tax break to consider too. :-)
7: Resist all temptation to use surplus capacity on the news server for
other functions, even on a temporary basis. "Temporary" installations
of stuff like web servers have an alarming tendency to become permanent.
8: The old news server isn't a total loss. You can usually find a use for
it as a ftp server or other type of server.
AB
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