This penguin walks on a bed of blue screens of death!

Lincoln Peters lincoln_peters at hotmail.com
Sat Oct 6 12:19:55 PDT 2001


>From: ME <dugan at passwall.com>
>Reply-To: <talk at nblug.org>
>To: talk at nblug.org
>Subject: Re: This penguin walks on a bed of blue screens of death!
>Date: Fri, 5 Oct 2001 23:03:44 -0700 (PDT)
>
> > On some day, ME wrote:
> > >That is good for the local server sysem, but only with the test
> > >server. Once you start adding clients and users using those clients
> > >booting, and loading files/libs, things will slow down.
>
>On Fri, 5 Oct 2001, Lincoln Peters wrote:
> > Is that still true if the libraries for the clients are all on the sdb 
>disk?
>
>Yes and no. If you have sufficient amount of memory on the server, then
>you can have the linux kernel (automatically) cache read-only files in
>memory and decrease disk access. Also, you can add memory to nicer SCSI
>cards for caching and possibly gain a little speedup for frequently read
>files on read-only filesystems. However, though SCSI card memory caching
>is faser than disk access, it is not as fas as kernel/memory caching for
>access times.
>
>If you have tons of memory, then mounted ramdisks with gigabytes of space
>and stuff copied from HD can work too.
>
>With only 16Mb of RAAM, I doubt you have sufficient space in memory for
>all of the services plus lots of disk caching for libs and such on the
>server side. (Clients may still be able to cache libs, but each client
>will need to read the lib at least once after boot, and the smaller the
>memory on the clients, the more likely they will need to re-read the same
>files fro he NFS share. Client caching will decrease the biggest slow-down
>(network) so lots of client memory is good for this.)

I tried upgrading the server to 32MB of memory, but I couldn't match the 
memory.  EDO memory can be *so* confusing!!!

>
> > Do you (or anyone else) know anything about bonding Ethernet devices?  
>If I
> > could get the other two NIC cards to do that, I'd re-install them.  If 
>the
> > network supports >10Mbps (I honestly don't know, but it should), 30Mbps 
>will
> > definitely be better than 10Mbps.  I would try to bump it up to 4 NIC's, 
>but
> > there aren't enough expansion slots for a fourth (unless I remove the 
>video
> > card).
>
>Um, channel bonding with ethernet may offer only a small amount of
>performance increase if the multiple interfacers all use the same shared
>ethernet segments/collision domain (Assuming HUB first). (All you gain is
>really increased chance for access to the media as you have 2 or more
>cards signalling for chances to rite to the shared media. On a busy
>network, this may hamper speed, as both cards may encounter use of CSMA/CD
>and do that whole back-off random times more often after collisions before
>attempting to re-send (both will likely have someting to send to the
>shared media at the same time.) Also, the overhead for the kernel's
>multiplexing and demultiplexing must be included even if it is fast and
>not "true multiplexing/demutiplexing" like "eql").

The kernel overhead alone may be enough to discourage me from trying Bonding 
(did I mention that it's a 486DX at 50MHz?).

>
>Channel bonding is likely more effective when multiple NICs each use their
>oen private ethernet segment to another server or less effective
>on separate private VLANs on a switched network, and even less effective
>on simple switched networks, but probably *way* more effective than a
>simple hub based/repeater only network.
>
><pre>
>ASCII Art: Here is how I believe that channel boding was
>originally supposed to work:
>
>Different private linkx for each host to host network:
>
>        |=NIC1a----NIC1b=|
>        |                |
>host1--|=NIC2a----NIC2b=|--host2
>        |                |
>        |=NIC3a----NIC3b=|
></pre>
>
>describes how I see channel bonding working optimally for ethernet from
>one host to another, or from one server to another.

And I doubt that anyone would be willing to install 2 more ethernets on the 
campus and 2 more NIC's in every workstation.  Although for some reason, 
they put two video cards in every workstation (but only supplied one monitor 
for each workstation).

>
><pre>
>ASCII Art:This is what some people see for channel bonding:
>(
>             ---HUB---NIC0b=|--host5
>                HUB
>        |=NIC1a-HUB---NIC1b=|--host2
>        |       HUB
>srvr1--|=NIC2a-HUB---NIC2b=|--host3
>        |       HUB
>        |=NIC3a-HUB---NIC3b=|--host4
>                HUB
>             ---HUB---NIC4b=|--host6
></pre>

I'm not sure how the network is laid out.  I know that each room has a 
4-port hub, and each one is connected to some kind of a router or switch.  I 
don't know how the routers are wired to each other.

>
>If the channel bonding uses cloned MAC addresses, and a HUB is used, I see
>loses in performance with multiple NICs competing for network access at
>the same time, and risk for collisions being higher. You also have
>processor overhead for recombination/sorting. The only speedup I see is
>network utilization. If one card is getting (burst max) 60% utilization of
>your network, and you add another card to the same collision domain, then
>you may be able to incease network utilization to say (guess) (burst max)
>80% between both cards, but at the cost of increased collisions, and
>performance degredaton for other hosts on the shared segment.
>
>Change the above "HUB" to an  "ETHERSWITCH" that keeps the MAC
>address/port/datestamp for each port, then a shared MAC may allow a
>greater performance increase than the HUB, but this may cause headaches on
>the side of the switch as you have mutiple ports with the same cloned
>MAC! the normal resolution on switches is to just update the insternal
>MAC/Port db to reflect the new changes to what MAC belongs to what port,
>and then send ethernet frames with a DST to that port instead of the old
>port that was in use before. But what does this do? The last port to send,
>is more likely to still be sending when an incoming ethernet frame for the
>"server" is meant to be sent to the server. This packet destined for the
>server cant make it to the server while the senbding port from the server
>is active and sending to the switch (even though the other "free" bonding
>ports might be available.
>
>If the switch creates virtual paths between ports for "connections" it
>sees in layer 3/4 (now layer 3/4 etherswitch has IP), and can manage to
>somehow remember that one session (oo another layer!) is assigned to one
>port, then you could have a higher layer of load balancing at the cost of
>packet inspection (delays/latency). This could be made to work with
>control to code your own layer 3/4 switch, but they are expensive, and
>what vendor will let you code thier firmware and let you have access to
>their specs? (There may be a complete package to do this out there an
>alieviate the need for you to code your own changes, but layer 3/4
>switches are more expensive.)

Nobody is going to be willing to get anything expensive (except, for some 
strange reason, Windows NT and Office 2000)

>
>Use of etherswitch options "store and forward" vs "cut-through" may offer
>some help for host that is sending on one interface and frames coming into
>the switch that need to go to the server, but each of those has their own
>impact on the switch too. :-/
>
>Using a switch in setting of VLANs where you have one NIC for each VLAN
>and then use the top diagram for two servers could possibly work, if the
>switch could work with the channel bonding.
>
>If you want the server to have all of its NICs share the same network
>segments as all of the hosts, then I see an Etherswitch as being more
>capable of making this "work" than a HUB,but would then question, "Can all
>etherswitches deal with cloned MACs on different ports equally?" and
>"Are there switches that allow you to 'break the rules' and assign more
>than one MAC per port, and send a frame with DST to that MAC on the port
>that is least busy?"
>
>This message includes a lot of "thinking online". Anyoe/everyone feel free
>to add your comments as I have not spent much time thinking about
>this. I know we have some networking people here, and some of them might
>have more insight to this. After all, I am still learning.

I think that you've scared me out of trying Bonding.  At this point, I'm 
just hoping that some day soon I'll be able to get a better server that 
supports 100BaseTX, or better.


_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp



More information about the talk mailing list