in case of low speed file transfer on file server, which parts of server should be suspected as bottle neck ?

I found that the transferring data speed is very low between serverA to serverB in my office.

I connected serverA and serverB directly,  link is up at Fast Ether , but the transferring speed is not enough. 50MByte takes 1 minutes.
I changed the network cable to see if network is no problem.
the result is same.

I suspect that ServerA's performance is not so good.
this ServerA is an appliance server, therefore I don't know what kind of CPU or memory are used.

In case of copy and paste data between folderA and folderB on the serverA,
50MB takes 2 minutes. ( it takes double time than network)

My question is ,
1)the reason of low data transferring speed is RAID1 ?( ServerA is Raid1)
If I change the Raid1 to Raid5, can I expect it is improved ?

2) Are there any possibility that RAID card is bottle neck ?
or SATA disk is bottle neck ? or
 low performance CPU ?
memory ?

which parts of server should be suspected as bottle neck ?

best regards