AW: [OpenAFS] Severe Performance Issue with SCSI!

[Daniel Clark/Cambridge/IBM]

> We are checking this with our infrastructure guys, but so far we beli=
eve
> that the switches as well as our network is doing all right (that is
> duplex).

Getting duplex settings right can be tricky - for example with the
particular combination of new Cisco routers and network cards at my sit=
e,
the only way to get 100baseT Full Duplex turned out to be to set everyt=
hing
to auto-negotiation. With the old Cisco routers, auto-negotiation didn'=
t
work, everything had to be set manually. The paper "Ethernet Auto-sensi=
ng:
Adventures in manual configuration" [1] is great. As has been mentioned=

this can easily look like an AFS problem instead of a network problem -=

usual tests of network throughput (using ftp, ping, etc.) tend to be hi=
ghly
unidirectional and can be seemingly unaffected by duplex problems. AFS/=
Rx
seem to be highly sensitive to network problems in general, so you may =
want
to try other network tests [2]. One thing you can try to determine if t=
he
performance problem is really an AFS issue is to set up your AFS server=
s to
temporarily also be NFS servers, and see if the speed problem still exi=
sts
over NFS. If you want to be somewhat scientific you can try running
postmark [3] against AFS and NFS using the same client to the same serv=
er,
once against AFS, then against NFS. Another cheap thing to try is to se=
t
the MTU on the server and client to something small - say 384 bytes - a=
nd
see if it makes any difference. If it does, some router is having probl=
ems
with packet fragmentation.

> Besides, we did the benchmark on different ports and segments of our
> network -- and the AFS server with IDE drives _are_ fast.

> Some AlphaServer, Tru64 UNIX 5.1 (IBM AFS) seems to perform well even=

> with  SCSI; actually this nearly 10 year old machine 10MBit interface=

> is even as fast as our fastest IDE-server running OpenAFS.

Are you saying you are getting less then 1 MB/sec performance even from=

your OpenAFS IDE boxes on 100baseT Full Duplex Switched ethernet? If th=
ere
is no other load on the network/systems you really should be getting at=

least 2.5 MB/sec on reads from AFS. If the most you can get is 10baseT
speeds - around 300-500 KB/sec - then something is seriously wrong, and=

it's probably the network.

[1] http://www-commeng.cso.uiuc.edu/docs/autosense/autosense.html
[2] http://www.oreilly.com/catalog/nettroubletools/
[3] http://www.netapp.com/tech_library/3022.html

--
Daniel Clark =A7 Sys Admin & Assistant Release Engineer
IBM =BB Lotus =BB Messaging Technology Group=