Hello If the disk is recognized in the BIOS then this is a software issue. There is likely a compatibility issue with the driver in Ubuntu, or there could be an issue with the file system. Make sure the file system is supported by the operating system. I would recommend booting to a RHEL or CentOS live CD/DVD to test functionality. If the drive works fine in one of those OS's then it is a driver issue in Ubuntu. Thanks
we are using a power edge 2950 server in our lab with 32bit Linux (Ubuntu 10.03 LTS).  4x250GB SAS drives using (3 of them are RAID5, and 1 is for backup).  And also a 3TB external HDD  (Single partition) is using for collecting some data via USB port. I tried to connected  the external HDD to internal SATA_A port. I've done the BIOS setup (it's updated) the system recognized the disk as 3000MB. But even the BIOS and OS (by fdisk)  are recognized the HDD I couldn't reach the files. What could be the problem? Here is the possibilities I think: 1) I can't use SATA_A or SATA_B ports to connect a HDD 2) there is a >2TB disk situation. (but I can use it via USB 2.0) 3) Because of the LINUX ver. (But I can use it via USB 2.0 again) 4) There is a partition type problem (512bit and 4096bit thing) Which is(are) the answer(s)? Is there any solution to connect 3TB HDD (or lover capacity) to use faster speed? Can I use a PCI exp usb 3.0 card?  
SATA HDD via SATA_A or SATA_B on Power edge 2950