copying data over NFS to raid5 array is jumpy

copying data over NFS to raid5 array is jumpy

[Dexter Filmore]

copying from a local standalone disk to a raid5 array works smooth at a 
constant 30MB/s. So far, so good.

Now, copying data from a machine on the network over 100MBit NFS is kinda 
jerky. It works, but within a second or two, the transfer rate reported goes 
from a few 100k/s up to 22MB/s (which is bogus - 100MBit=12.5MB/s max) and 
back, varying all over.
Copying to the single disk works is constant around 10MB/s.

I use "sync" in exportfs for all shares.

What could cause this behaviour?


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