by Tom Nelson
I’ve heard it said that an SSD or hard drive that isn’t used for extended periods of time will likely have performance issues, or worse, actually lose data in the span of a few years. I’ve even heard it said that SSDs could lose their information in less than a year, and in the worst case, within a few days.
Of course, I’ve heard a lot of things, and not all of them bear up well when looked at closely. So, let’s find out if we need to keep exercising our storage devices to maintain information and performance.
Data Retention
The ability of a storage device to keep the data it contains intact is known as the data retention rate. The actual rate cited for various devices is predicated on the storage device being non-powered, undergoing no refresh of the data it contains, and being kept in an ideal storage environment, usually mentioned as around 25 C / 77 F.
Under those ideal conditions, hard drives are predicted to be able to retain their data for 9 to 20 years. The long range is due to the different architectures used in the manufacturing of modern hard drives.
SSDs (Solid State Drives) have a reputation for having a very low data retention rate. Numbers commonly cited suggest one year for consumer grade SSDs, and as low as one week for enterprise class SSDs.
If you believe the reputation is true, then SSDs would need to be exercised at defined intervals to ensure they keep the data stored intact. However, is that reputation valid? We’ll find out in a bit, but first, let’s look at hard drives.
Hard Drive Failure Mechanisms
The length of time your data will be retained on a hard drive in storage, one that isn’t powered and kept in a controlled environment, is based on four primary factors:
Magnetic Field Deterioration: Permanent magnets generally lose their field strength at the rate of 1% per year. After 69 years, the field strength would have dropped by 50 percent. That much field strength loss will likely lead not only to general data corruption of the stored data, but also to the loss of the index tracking marks which tell a drive where a sector starts and stops. So, not only is the stored data lost, but the ability to read the drive may be gone as well.
Magnetic Field Corruption: Magnetic fields external to a stored hard drive can adversely affect the stored data by altering the charge at one or more locations on the drive’s platters. Magnetic disruption can be caused by nearby high power magnets, motors, or even by unusually strong geomagnetic storms caused by solar mass ejections on the sun.
Environmental Conditions: Humidity and temperature ranges for stored hard drives differ by drive manufacturer. Western Digital recommends storing their hard drives between 55 F and 90 F. Extreme high temperatures increase the risk of damaging mechanical components, such as warping heads or platters, while extreme cold temperatures can cause bearing failure, or allow the spindle and motor to become misaligned. (Related: Keep Your Electronics Warm and Safe This Winter)
Mechanical Failure: Even with the proper storage conditions, mechanical failure, such as the platters failing to spin up due to motor failure, or spindle bearing failure, can happen. These types of failures tend to occur when drives are stored for exceptionally long periods of time without ever being powered on.
Mitigating Hard Drive Storage Failures
Of all the possible issues with hard drive storage, two of the most common ones can have their effects mitigated by exercising the drive. In the case of mechanical failure over long time frames, the simple approach is to power on the drive occasionally, ensuring the bearings, motor, and grease are all warmed up, and preventing them from becoming stuck in one location.
Refreshing the stored data can reduce magnetic field deterioration. This would require the drive to be powered on and connected to a computer system. Reading the stored data isn’t enough; to refresh the magnetic charge the data must be read and then rewritten to the drive. An easy way to accomplish this, assuming there’s enough room on the drive, would be to copy the content to a new location on the drive, or create a disk image and copy that to a new location on the drive. Another option would be to clone the drive to another storage device, and then clone the drive back again.
How often you should perform this exercising of a hard drive is difficult to say, but once a year or once every two years would be a good starting point. While a longer time frame is actually possible between exercising a hard drive, the task tends to get overlooked when the time frame becomes longer. It’s much easier to remember a yearly exercise routine than to try to remember to perform this task once every x number of years.
Screen shot © Coyote Moon, Inc.
SSD Failure Mechanisms
A few years back, a presentation was made at the JEDEC Standards Committee for solid state drive requirements at which a slide showing expected data retention rates for SSDs in a powered-off stored state was shown. That slide indicated the very poor ability of an SSD to retain data for any length of time when powered off. Specifically, it mentioned the following data retention rates:
Consumer grade SSD: 1 year at a 30 C storage temperature.
Enterprise grade SSD: 3 months at 40 C storage temperature.
In both cases, as the power off storage temperature increases, the data retention rate falls. In the case of consumer grade models, data retention can fall at one month at 50 C, while enterprise class SSDs can see less than one week at 50 C.
Pundits quickly picked up this information and it spread around the Internet, leading to the poor reputation SSDs can have for data retention when powered off. The problem is that it’s simply not true. The information being conveyed in the original presentation pertained to a worst-case scenario, one where the SSD under question has nearly reached its end-of-life, and has had its P/E count (Program/Erase cycle count) reach the point where data cells would start showing write failures. But when the background information was removed and only the information on the slide was presented, a legend, or at least a reputation, was born.
