The HDD Deep Dive

• HDDs are measured in how fast their platters (magnetic disk where data is stored) spin
  • Most are either 5400 or 7200 RPM, with some enterprise up to 15000
  • These read at ~80-160MB/s
• HDDs were traditionally made with Conventional Magnetic Recording (CMR) where the read and write track are the same width
• Some HDDs now use Shingled Magnetic Recording (SMR) where the read track is narrower than the write track
  • This allows data to be more densely packed since parts of the data can be overwritten without data loss
  • Write speeds are similar to CMR but degrade greatly when the drive runs out of cache space
  • These are usually less expensive
• Manufacturers publish whether or not a HDD is CMR or SMR, but they’re not happy about it
  • Some drives come in both a CMR and SMR version