You can't do that with a SAS 6/iR controller. The SAS 6 is a low-end controller with very limited capabilities. 1) you cannot expand the size of an existing array, and 2) you cannot have multiple arrays across the same set of disks. The PERC 6/i controller is a high-end controller and would afford you more flexibility and options but is not officially supported in a T105. With the PERC 6, you could create a second array across the disks (would be presented to the OS as a separate "disk" for storage). Your "best " option is to do a backup, create a new, larger RAID 1, and restore the data to it.
I have a Dell Poweredge T105 with a SAS 6IR controller. It is running Windows Server 2008 R2. It has a 40Gb C: drive which has the OS on it. The D: drive is used for data storage and uses the remainder of the capacity of the drive. Because of low disc space I have replaced the original Western Digital RE3 500Gb drives with Western Digital RE4 2Tb drives, they are configured as a RAID 1 array. After allowing each drive to rebuild I was still showing a 500Gb array which I understand should be the case. When I look in the Windows UI for the controller it shows the extra 1.5Tb on the rives as reserved, Windows explorer and Disc Management only show the 500Gb and no unallocated/free space. Also the negotiated speed for the new drives is showing as 1.5Gb instead of 3Gb. My questions are:- 1. Can  I utilise the extra 1.5Tb without loosing data. How can this be done? 2. How can the drives be made to negotiate at 3Gb. Thanks in anticipation.
Unable to use extra storage space on replacement HDD