Akther, You can connect the additional MD1000 without ruining the VD that have been configured. They will show up as unconfigured until you assign the new drives to a VD. Below is a link to a PDF that show all the supported configurations. It starts on page 8.  support.dell.com/.../md1000_SupportMatrix.pdf Please let me know if you have any other questions.
Hi We are looking to add one more shelf ( MD1000) in to existing Dell Power Vault MD1000 SAS Array ( DAS) . There are 2 RAID 5 virtual disks already configured in existing MD1000 box. We need to make sure that it will not ruin existing configuration. And SCSI cable is connected from MD1000 Out port  to Server ( Dell PoerEdge R710) In ( both out to host PERC 6E controller). Can some assist how we can go ahead to add one more MD1000 to esitsting infrastructure      
Adding MD1000 to existing MD1000 Array