[OpenAFS] Re: WAN speed

[jukka.tuominen@finndesign.fi]

Hi all,

here are some ping results outside LAN:

1.62  1.80  1.62  2.33  1.69  1.64  1.75  2.35  5.77  3.85  4.69  2.73 ...

The internet speed is the same 100/5.

I just moved ~20M/~2000 files
  AFS to SSH server ~220KB/s
  SSH server to AFS ~80KB/s

The client was in WAN this time, whereas both servers where in the same
LAN (not sure it they knew it :).

br, jukka









> The lacks large window sizes is unlikely the issue in this case.  The use
> case is reading large numbers of small files which require a separate RPC
> for each object.  An 8MB window size won't help when the file sizes are
> small and the number of files is large.  The RPC latency * number of RPCs
> is what matters.
>
> Jeffrey Altman
>
>
> On Mar 22, 2012, at 11:28 AM, Simon Wilkinson <simonxwilkinson@gmail.com>
> wrote:
>
>>
>> On 22 Mar 2012, at 15:23, Andrew Deason wrote:
>>
>>> On Thu, 22 Mar 2012 15:20:20 +0000
>>> Simon Wilkinson <simonxwilkinson@gmail.com> wrote:
>>>
>>>> That limit is imposed because it is the point at which the current RX
>>>> implementation loses the queue efficiency/throughput tradeoff. You can
>>>> run with a larger window size, but it will actually make things go
>>>> slower.
>>>>
>>>> It was naively increasing the maximum window size to 255 that caused
>>>> the huge performance problems in the 1.5.x series that Andrei
>>>> highlighted at the 2010 European AFS workshop.
>>>
>>> Yes, I know, that's what I'm talking about. Even if we didn't have that
>>> problem, a window size of 255 is still prohibitively small for many
>>> uses.
>>
>> Yeah, that's a bigger problem. We can't extend the window beyond 255,
>> because that's the maximum size of the RX ACK packet.
>>
>> Large windows only help up to a point, though. We go back in to slow
>> start with every new call, (this is similar to TCP, which re-enters slow
>> start if RTT has passed since the last packet was sent). So, you will
>> only use the full window for Store or Read Data if you are writing
>> enough data in single call that you can grow the window quickly enough.
>>
>> Ultimately, we either need rx/tcp, or a bigger revamp of rx/udp than
>> anyone is currently considering.
>>
>> S.
>>
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