Why does the capacity of 1TB SSD shrink to 953GB? Does it turn corners in production?

Some users who have just bought SSD may be doubt for the capacity label of SSD. Samsung 860 PRO 1TB SSD, whose capacity is equal to 1024GB in theory, is just 953GB in computer, and some SSD even is below 953GB. What is this situation? Does it turn corners in production? That is not the real answer.

If we want to understand this question, we should begin with the SSD working mechanism.

The available capacity of 1TB SSD is 953GB

People who buy SSD will hear the concepts of "balanced reading and writing" and "garbage collection" more or less, which are based on a module called OP reserved space.

As we know, initial-date will be erased when SSD writes. So in order to avoid filling up invalid pages in SSD, the garbage collection function of its controller uses OP reserved space as temporary workspace to manage planned invalid page merging and reclaim blocks filled with invalid or deleted pages.

These collection pages and blocks added in reserved space can help SSD controller to write ensuring the performance of the hard disk during the maximum load period.

SSD will be slower, because reading, erasing, modifying all invalid pages and writing them back to blocks that have partially filled in invalid pages on SSD can have a significant impact on performance.

With reserved space, the available blank blocks provided by the reserved space storage capacity can help maintain effective wear balance on NAND flash, because the SSD controller can intelligently distribute write operations evenly on all NAND flash chips without affecting the SSD overall performance during high traffic loads.

In addition, ATA data management TRIM command can increase the SSD available space by recycling any invalid pages and unused user capacity.

Therefore, OP reserved space is significant for SSD. We had better not think about a few percent of space.

There are three OP reserved space. The first is due to the unit conversion problem. The nominal capacity is in the megabyte, that is 1GB is equal to 1000MB. While NAND flash are 1024 binary system where 1GB is 1024MB. Among them, the space value of the difference is the first layer capacity, which can not be changed, and is also fixed for all brands. The difference is about 7.37% of the nominal capacity of SSD.

The second is due to products' orientation from SSD design and master manufacturers. For example, the reason why 256GB SSD appears 240GB/250GB/256GB, or even 200GB lies in the different manufacturers' setting for the second layer OP capacity.

We can't say absolutely that the second OP capacity is greater, the performance of the product is better. We can only say that the more the second OP space is reserved, the better the performance of solid-state controller mechanism such as garbage collection recovery and wear balance can be improved to improve and maintain the long-term high speed of SSD without slowing down.

The third OP capacity where can choose to set the space is similar to the second

However, SSD price is respectively expensive, because OP space installing will reduce the SSD actual available space especially in early stage. So many client SSD canceled the third OP space. Most SSD has their own third OP space and some brand has supported to installed OP space by themselves.

Next, I will show you how Samsung 860PRO set OP reserved space which is very easy.

Samsung 860PRO

If you install Samsung SSD OP reserved space, you should firstly download Magician APP which is official SSD management software of Samsung.

Magician
We can look up some relative information about SSD like writing capacity and firmware versions. Here we click "Over Provisioning" below.

Then clicking operation Over Provisioning to enter the page of OP reserved space.
Installing OP space
It should be noted that OP space installing should be between 1% and 50% of hard disks capacity. For light users, 1% is enough. Even heavy users, 10% is maximum. After all, the capacity of each GB is purchased by money, It is very wasteful to set up large OP space.

Ok, that is some about SSD OP reserved space.

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