Poor write performance with Dell PowerEdge R410 and RAID 1

Hello everybody, first time poster here.

Our customer complains about poor database application performance and is right about it. In fact, if we restore the database on our system (or virtually any other system, even an old laptop), we experience about ten times better perfomance as compared to the customer's server, so it is hardly related to the database structure. After some investigation (SQL profiler, performance counters) we narrowed the question to the write operations, which are much slower on the customer's server, but we have no idea why (there is no significant difference for read operations).

Customer's hardware: Dell PowerEdge R410, one quadcore Intel Xeon E5506 2.13 GHz, 16 GB RAM (DDR3 800 MHz), 2x 1TB SATA Hard Disk 7.2K (Seagate ST31000524NS) as RAID 1, 64K strip size, SAS 6/iR integrated controller.
Customer's OS: Windows Server 2008 R2 Standard
Customer's SQL Server: MS SQL 2008

Any clues?

Welcome to forums
I am not an expert in Dell hardware, but I suspect an hardware issue here. IF the RAID controller's cache is not enough, RAID 1 can be slower than directly connected disk.
From the documents I searched, I couldn't find that piece of information.
I suggest you to contact Dell agent on this.

Thanks for the suggestion. Currently we negotiate with the customer switching to another server and/or restructuring the RAID array. We'll try to contact Dell agent, as you suggested.

Just a logical flow of my thought process. Hope it may add some value to you when negotiating with the client and their vendors.
Physically you have only two disks and they are configured as mirror. That means, irrespective of the activity (OS level, log file data reads/writes) the disks will be busy. But single disk may not be the issue as it works even on single disk Only difference I see with a single disk and RAID 1 is it needs to write to both disks. That to get slower, the controller may be waiting or at OS level you are getting a problem. At times I have seem OS level bottleneck if we have only one LUN even if we have multiple disks. If it is not the issue at OS level, it should be from controller.