Hi If we have 18 15k disks in a raid 10 setup for sql-server data using ibm ds4300 (without turbo). We are currently seeing around 17,3 as avg disk queue write length during peak hours. We dont have any read queue length. Would an upgrade to ds4700 improve the performance, or would it be better to buy another expansion unit (exp 810) with 16 disks, so we get 18+16=34 spindles? The difference of ds4300 and ds4700 is 4Gbps instead of 2Gbps bandwith (the hard disks that we have is 4gb disks) and more cache on the controllers.