Do Magnetic Disks Really Last Longer Than SSDs?

Calendar with pages flying off of it next to a hard drive and a server

Posted on Friday, June 14, 2019

When it comes to speed of storage, SSDs will beat hard drives every time, which explains the steady move towards all flash arrays (AFA). But is the same true in terms of durability and longevity?

The issue of SSD degradation

The fact that SSDs have a limited lifespan is well-known. Every data write operation has a degrading effect on the memory cells, eventually leading to unusable blocks and eventual failure. Knowing that the internal drives are literally failing a little more every day leads to questions about longevity of AFAs. 

Hard disk drives (HDD) are completely different. Because data is written by manipulating magnetic fields on a spinning platter, the disk (in theory) never wears out– it could operate indefinitely.

Experience shows this to be untrue, however. The platters in a disk may remain perfectly functional but moving parts (spindle, bearings, motor, actuator) will eventually wear out, causing the entire drive to fail.

But which will fail first?

It depends…

Unfortunately, comparing failure rates isn’t easy. Hard drives lifespans are measured in hours, SSDs in write operations. So a hard drive may last years, while an SSD lasts hundreds of terabytes. 

The longevity of an SSD is determined by how much data you write every day. If a flash disk is capable of writing 700TB of data before failure, the question becomes ‘how long would it take to write 700TB of data under normal operations?’ Using stats published by TechReport, if your applications write 40GB of data each day to 256GB SSD, the unit may last up to 17,500 days (49.1 years).

Obviously these figures will vary between manufacturers, but it is clear that SSDs last much longer than many people expect. Especially when just 60% of hard drives make it to their sixth birthday.

The future is bright for AFAs

For business operations defined by speed, SSDs have been a clear winner for some time. But as the myths about longevity are dismantled, it is becoming clear that investments in all flash arrays will pay dividends in any deployment scenario.

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