aberdeen data recovery

CMR Vs SMR Data Recovery

Mechanical hard drives are still popular but their target market has changed.   Most new laptops and desktops shipped today comes with Solid State Drives, usually of the NVMe variety.  These are fast and robust but not generally of huge capacity as they cost more per GB than mechanical drives.  Typically they range from 250GB to 1TB, which for most people is more than enough storage on their laptop or desktop. 

Some consumers and many businesses require larger amounts of storage in either servers or NAS units and so the battle to fit as much data onto a spinning drive has continued with new drives storing as much as 20TB on their spinning platters.

aberdeen data recovery

 

Two storage technologies are available for mechanical storage, those being CMR and SMR.   CMR stands for Conventional Magnetic Recording which is really actually ( at least in modern drives) PMR, Perpendicular Magnetic Recording.  Well suited for applications where lots of reads and writes occur, data is written to magnetic tracks on the platters, these tracks are separate and do not overlap.  This setup means data can be quickly and reliably read and written without disturbing the data stored around the required track.

 

SMR drives use Shingled Magnetic Recording.  Just like shingled roof tiles, each track overlaps with two other tracks. In this way, storage density is increased meaning more data can be stored on a single platter, however, it comes at the expensive of increased complexity and writing performance.   When data is written to an SMR track, it will also overwrite the data stored on the next track, this means the drive has to first cache the data from those tracks and rewrite it if necessary. 

If the whole drive was full of SMR tracks, this would mean that if any data was written to the disk, this arrangement would require all subsequent tracks to be read and rewritten, not a very efficient way of writing data! 

This can slow write performance down significantly if large files are transferred to the drive.   The drives do contain a faster cache that helps to mitigate this, however once the cache is full, a significant speed decreased can often be seen.

From a data recovery perspective, SMR can and does add extra complexity to a recovery case though with proper tools, data recovery is still usually possible.  

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