Date: Sat, 18 Jan 2003 14:52:28 -0800 From: Lars Eggert <larse@ISI.EDU> To: Terry Lambert <tlambert2@mindspring.com> Cc: Scott Mitchell <scott.mitchell@mail.com>, Jay Sern Liew <jay@americanhorizonsbank.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: 5400RPM|7200RPM Cable bottleneck? Message-ID: <3E29DAAC.5040707@isi.edu> In-Reply-To: <3E29D4D2.47A5E909@mindspring.com> References: <1042849118.3e289d5ee4458@webmail.americanhorizonsbank.com> <20030118105015.GB783@fishballoon.dyndns.org> <3E2998FD.1010904@isi.edu> <3E29D4D2.47A5E909@mindspring.com>
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[-- Attachment #1 --]
On 1/18/2003 2:27 PM, Terry Lambert wrote:
> Lars Eggert wrote:
>
>>I've tried NFS mounting ISI servers at home over PPTP over a cable modem
>>connection, and it's painfully slow - much slower than the bandwidth of
>>the cable pipe. NFS isn't well tuned for high-RTT environments (in my
>>case, 20ms).
>
> The up-channel speed on a cable modem is usually in the
> neighborhood of 1.5 times the amount of bandwidth needed
> for just the ACKs for the data coming down the down-channel;
> that leaves very little bandwidth left over for NFS requests
> to the server, particularly if there are a lot of data
> transfers taking place from the server to the client (client
> reads). If you are doing any level of data transfers from
> the client to the server (client writes), you should expect
> your performance to go to hell.
Both uplink and downlink bandwidths are nowhere near saturation - it's
the underlying RPC that make NFS inherently slow over WAN links.
Lars
--
Lars Eggert <larse@isi.edu> USC Information Sciences Institute
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