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HDD vs SSD – which lasts longer?

HDD vs SSD

Many comparisons can be made between a Hard Disk Drive (HDD) and a Solid State Drive (SSD); cost, speed, data storage capacity – there’s no end of areas to consider. However in this post, we’ll be looking specifically at the durability of HDDs and SSDs to assess if there is any difference in life expectancy between the two data storage types.

Physical failures

It’s important to firstly note that any life expectancy figures for HDDs and SSDs alike cannot be 100% guaranteed. These estimates assume manufacturer’s recommended environmental conditions and do not take into consideration extremes of temperature, humidity and physical mishandling. In fact, out of almost 2000 devices surveyed between January and March 2016, at least 30% had sustained some form of physical damage to cause the media to stop working and/or cause data loss.

HDDs are electromechanical devices – they have moving parts – which generally makes them more susceptible to damage from a physical shock. However many modern hard drives, particularly those destined for the mobile device market, can withstand extremely large physical shock when the heads are parked and incorporate shock-proofing technology such as free-fall “drop” sensors which are used to protect the heads and media even when the drive is running. Although SSDs have no moving parts and are more robust in this respect, the use of NAND flash memory as a storage medium brings with it a whole host of new complexities and therefore the possibility of data loss for reasons other than physical shock. It is therefore a myth that SSDs cannot suffer from a type of physical failure.

Loss of power

So what would happen if you just left the devices… to their own devices? Many of us would assume that if you simply did nothing and left a drive in average storage conditions (temperature, humidity, etc.) then no data would be lost, right? Well this is actually not the case; data stored on a HDD will gradually degrade as the magnetic domains representing the bits of the data change polarity, increasing the number of ‘bit errors’. But if we assume normal storage conditions, data stored on a HDD will degrade far more slowly that data stored on a SSD that uses NAND flash memory. Why? NAND flash stores data as electrical charges, which leak away relatively quickly in comparison with changes in magnetic domain polarity – it’s due to the imperfect insulation within the structure of the memory itself. However with SSDs, data degradation (that is sufficient enough to prevent the correction of stored data with ‘Error Correction Algorithms’) should not occur for at least 10 years if the drive is left powered down in optimum storage conditions. This timeframe does, however, depend on the type of NAND flash memory used, for example ‘Triple-Level Cell’ (TLC) memory can actually lose data far more quickly – even as soon as a few months.

In fact, data loss from NAND memory can still occur even when the memory is powered. Good SSDs use a background refresh technique to restore the charge in cells that are identified as marginally retaining the data. Some areas of the NAND flash memory are reserved for use by the drive’s operating code and data, known as firmware. Firmware is read every time the SSD is powered on but some portions are not re-written regularly. Although manufacturers may take steps to mitigate the effects of cell charge loss (i.e. using a less-sensitive cell charge threshold for NAND cells that store firmware and periodic refreshing of cell charges), if excessive bit errors do cause firmware corruption the SSD can stop functioning altogether.

How does this compare to HDDs? Well, every 10 years or so some of our engineers have been successfully booting up and reading data from HDD systems that are well over 30 years old – error free!

Storage of storage

What about storage conditions? Can factors such as temperature and humidity affect the retention lifetime of stored data on HDD and SSD? In short – yes – no storage media will last forever. High humidity, for example, can be a significant problem for both SSD and HDD as it can lead to the oxidisation and corrosion of metals. However high storage temperatures have a significant effect on SSD data retention; the rate of data degradation in NAND flash memory accelerates considerably with increased temperature.

For the average use of a laptop or mobile device this area probably isn’t going to be an issue, but when you start looking at servers and data centres adequate media storage conditions are required to protect against drive failure (and potentially data loss) as a result of overheating or high humidity

Should I be worrying?

The reality is for normal day-to-day usage in a laptop or PC, for example, you needn’t lose sleep over the life expectancy of your storage media. Aside from an incredibly small proportion of manufacturer defects, your HDD or SSD shouldn’t give up on you easily if you’re taking care of it and keeping it away from physical hazards. If you’d like to investigate more there are many different ways to monitor the logical health of your devices; there’s ‘SMART’ tools to predict drive failures and software to check the wear and tear of SSDs in detail, including how much usable life it has left.

With mobile devices, there is obviously a higher risk of physical damage (dropped phone on the floor, iPads taking a bath, etc.), but with normal, everyday usage, you would be highly unlikely to encounter issues in the longevity of the storage media itself. If you’re looking to store data longer-term then it might be best to go HDD over SSD, or better yet – look into the wonderful world of magnetic tape storage (yes, they’re still used!).

If you’re looking for further guidance on which storage type is best for your business, it’s worth also checking out this article, which puts HDD and SSD technology against each other and adds the more recent ‘hybrid’ storage type into the mix.

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