DriveDx reported the SSD I use very rarely for Snow Leopard at 35% of its lifespan. As it's over five years old, that's not surprising. But what did surprise me is that the 80Gb IBM SSD that I keep on the shelf as backup for the SL drive was reported as excellent over the USB connection and it is over eight years old! I guess it is lasting longer because it is not powered up all day?
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the 80Gb IBM SSD that I keep on the shelf as backup fo the SL drive was reported as excellent over the USB connectionâ“â“
Please elucidate! The USB standard does not support reporting SMART values. How were you able to accomplish this feat of legerdemain?
SSDs have no moving parts — rotating disks, moving read/write heads, bearings,
etc. — that wear when the drive is powered up. The biggest wear factor for SSDs is the number of Write operations to the drive. A data segment on an SSD can only be written/re-written a finite number of times before it will no longer accept a write operation. There are a number of techniques to even out the wear on the drive (for details see
this Wikipedia article) and there are spare sectors built into every SSD that can be mapped in when a well used sector reaches its limit. "Wear" is therefore measured by the percentage of spares that have been used, and the % remaining available spares. As long as an SSD is primarily being read and seldom, if ever, written to there is nothing creating wear and so it theoretically could last generations.
WARNING: While an SSD could theoretically last generations, that is not true of the data written on the SSD. All electronic data storage deteriorates over time and SSD data deteriorates faster than most. Experience and tests have shown that data on industrial grade SSDs begins to deteriorate in as little as two to three years and for whatever reason consumer grade SSDs can go as long as four years and still be reliably readable. The point is, if you are using SSDs for long term historical or archival storage of data, the data needs to be "refreshed" (re-written) every few years to maintain its integrity. Data on magnetic media such as Hard Drives is longer lived but HDs are not immune to data loss over time either. I suspect your eight year old backup drive has lost some, perhaps a significant amount of its data integrity over the years. The drive is still perfectly usable but the data would be suspect. That is why I don't recommend SSDs for Time Machine and other backup media. HDs are still a LOT less expensive, retain data integrity longer, and speed is not a significant factor for backup purposes.
