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[Nbd] Performance tuning of nbd !?

Hi! I'm a big fan of nbd and using it for quite a while. In my standard 
setups of local ethernet LANs it performs well. I did some measurements:

  10MBit/s:  hdparm -tT gives me ~1000kByte/sek.
 100MBit/s:  hdparm -tT gives me ~5-6.2MByte/sek.
1000MBit/s:  hdparm -tT gives me ~23MByte/sek.

measured on an average Core Duo, Intel board with Gig of RAM. Server 
(single Opteron with 4GByte of Mem, low load) and client are on the same 
subnet (one or two switches in between). Checked all values with dd 
reading of 10MByte linear from device - nearly same results.

When it comes to WAN connections (higher latencies) the performance drops 

~100Mbit/s bandwidth (at least) between server and client and the 
performance drops to ~520-750kByte/sek.

When I try it over cable (okay, might be a little bit perverted - 25Mbit/s 
ping of 15ms) or DSL (14Mbit/s ping of 35ms) the results drop to less than 
200kByte/sek. It is still possible to run a stateless client that way 
(squashfs ontop of nbd), but you have to be patient while an app is 
starting the first time.

Is there any chance to get above the 10Mbit/s LAN rate in the WAN DSL or 
cable scenarios!?

Thanks!! Dirk

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