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SSD vs. HDD
SECURITY SHELF

SSD vs. HDD 

It is difficult to argue against using an SSD in a laptop. Some manufacturers offer SSDs as an option while Apple uses SSDs exclusively in their current Macbook lineup. Many users have replaced the HDD in their laptop with an SSD to improve performance and increase the length of time they can operate unplugged. SSDs have also become more popular in datacenters. Amazon, Google, and Microsoft Azure allow public cloud customers to choose SSD or HDD. Other providers, such as Digital Ocean, offer only SSDs.

An obvious disadvantage cost; SSDs are approximately twice the price per GB. However, that doesn’t take into account power and cooling costs. Another disadvantage is that 8 TB HDDs are commonly available, while leading-edge SSDs top out at less than 4 TB. The biggest concern with SSDs is reliability and whether data can be recovered in the event of a drive failure.

David Zimmerman, CEO of LC Technology International, has extensive experience recovering data from SSDs. His company makes data recovery software for SanDisk and others. Zimmerman explained that recovering data from SSDs is very difficult due to the complexity of the devices. In some cases, experts have been forced to resort to XRAY to pinpoint where the failure has occurred.

According to Zimmerman, SSDs are much more complicated than HDDs. The controller stripes data across multiple chips, and must maintain a mapping between the track and sector used by the disk controller and the actual internal location where the data is stored. Controllers use different write patterns, and the manufacturers are very protective of this information. Since each cell can only be written a finite number of times, SSD controllers implement wear leveling in an attempt to use cells evenly. Like their HDD cousins, SSD controllers also must keep track of cells that fail in the same way that magnetic drives maintain a bad sector map.

Many SSDs also use hardware write caching to improve performance. However, if the cache contains too much data when power is lost, data corruption may occur. This can potentially impact the internal data used to locate data within the SSD. Zimmerman has seen SSDs “bricked” when power was lost during a write operation. The issue is significant enough that some SSDs now include capacitors to store enough power for writes to complete.

As a result of this complexity, Zimmerman estimates that only 20 to 30 per cent of SSD data recovery attempts are successful. With an HDD, a technician can physically remove the platters and re-install them in a working drive if required. That option simply does not exist with SSDs.

SSDs should be able to read from their cells forever, but as previously mentioned, each cell can only be written a finite number of times. In theory, Zimmerman explained, a SSD is supposed to know when it is likely to deplete itself of writable cells. However, SSDs haven’t been around long enough for people to have them fail from age.

One question often posed about SSDs is how they will behave when left powered off for an extended period of time. It is possible that data quality may decrease. In response to this question, Zimmerman made an excellent point: From a practical perspective, it doesn’t make sense to use SSDs for offline backup when HDDs are much less expensive.

Zimmerman recommends that businesses purchasing SSDs consider what, if any, support tools the vendor makes available. For example, is the ability to upgrade drive firmware, wipe the drive, clone data, and report wear information provided? Some SSD controllers report lifespan as a percentage, some do not.

As there are no moving parts, heat, vibration, and mechanical wear are not issues for SSDs. Monitoring S.M.A.R.T. status is advisable, but when SSDs fail, they tend to do so suddenly. SSDs have many advantages, but users must understand the disadvantages and exercise vigilance with backups.

Have a security question you’d like answered in a future column? Email eric.jacksch@iticonline.ca

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