HDD performance is slow in ubuntu

Thanks for posting the Output,

The above results suggest that they have already crossed their Threshold values, it would be wise to take backup , and Replace it if is under Warranty period. Further pressing to get the desired performance may damage it.

Reallocated Sectors Count showing 736 , While primarily used as a metric of the life expectancy of the drive, this number also affects performance. As the count of reallocated sectors increases, the read/write speed tends to become worse because the drive head is forced to seek to the reserved area whenever a remap is accessed.

Spin Retry Count showing 202 It is the count of retry of spin start attempts. This attribute stores a total count of the spin start attempts to reach the fully operational speed (under the condition that the first attempt was unsuccessful). An increase of this attribute value is a sign of problems in the hard disk mechanical subsystem.

For further reading refer here and S.M.A.R.T. wiki

P.S: A low health value alone does not neccessary mean that the hard disk will surely die in the near future (to verify this, a complete (hardware) examination is required), but there is a real chance for failure.

I consider any drive showing a non-zero value for Reallocated Sector Count or Reallocation Event Count to be a candidate for warranty replacement. Combined with the inability to detect the drive in SATA mode, I think you have a bad drive. If it is still under warranty, have the drive replaced.

Replace the drive. Any drive that has bad sectors is doomed to fail some day.