What damage have I done to my SSD drive by defragmenting it?

Q A review of a solid-state disk (SSD) in Computeractive issue 340 stated that SSDs should not be defragmented.

As a long-term user of an Asus Eee laptop, one of the earliest netbook-style computers fitted with such a disk, this advice unfortunately came a little too late. Could you please tell me what defragmenting will do to the SSD, what damage this will cause and how it can be repaired?
Shane McLaughlin

A Don’t panic – your SSD is unlikely to go kaput just because you have defragmented it a few times.

But it is true that you should not defragment SSD drives. What is more, defragmenting an SSD can indeed be detrimental to the drive’s health, but this is a long-term, rather than short-term issue.

Without getting too technical for what needs only to be a short answer, SSDs employ a technique called wear-levelling to ensure that all the data-storing areas of the drive are used evenly over the life of the device.

Running a defragmentation tool – such as Windows’ own Disk Defragmenter – disrupts this drive-managed wear-levelling, meaning some storage areas end up being used more than others. The result is that the drive could fail earlier than would ordinarily be expected.

As for repairing the ‘damage’, there is nothing to be done. With frequent defragmenting, some areas of the SSD’s memory may have been written to and erased more than other parts – so they are more worn.

However, the harm caused is broadly theoretical and is spread over the disk’s memory chips. As SSD drives are designed to withstand hundreds of thousands or even millions of erase-write cycles, it is likely that you will have replaced the netbook before its disk even reaches its expected failure point.