Exceptional slow batch operation for Azure Table

Question

I have a VM Medium with an Azure Storage.
West Europe
Same Affinity Group
Different storage account for VM and for my application
I noted that today, during the afternoon, my storage became very very slow all of a sudden.
I was happily uploading my batches with the rate of 2 MB/S, and now, suddenly this afternoon, I started to get better than 300KB/S.
I noticed that my network and CPU activity were very low.
I started Fiddler, and seen that my batches of 100 KB approximately took 14 second to upload !
I tested the same program on a VM in a different subscription with different affinity group, the same exact same batch took 200ms approximately.
What can do enjoy my full speed again ? Seems like a mouse is eating the cable of my rack.

Answer 1

Update :
I eventually it the threshold with a new table, my insert on the other table are starting to take more than 2 seconds to process, and it goes up with time.
So, insert is not constant, but depend on partition's size. Is it normal ?
Niranjan Nilakantan of Microsoft said
If the key for your logical data model has more than 1 property, you should default to (multiple partitions, multiple rows for each partition).
If the key for your logical data model has only one property, you would default to (multiple partitions, one row per partition).
We have two columns in the key to separate what defines uniqueness(PartitionKey and RowKey) from what defines scalability(just PartitionKey). 
In general, write and query times are less affected by how the table is partitioned.  It is affected more by whether you specify the PartitionKey and/or RowKey in the query.
If this is true, there is a real problem with my storage node.