SSD AND SMART WARNINGS

SMART was originally developed for hard disks using the IDENT command. IDENT provides operating hours, sector count and spare sector use among many other fields.

IDENT is a 512 byte block patterned over the original sector size of hard disks long ago. Fields vary with some larger ones for product name and serial numbers. Many are bit fields so some parsing is needed to read the values.

kingdian-m.2-ssd

SSD have adopted IDENT so that users can monitor factors such as the TB written. Unlike hard disks, SSD use a bank of NAND cells that eventually wears and no longer can provide data accurately. The mechanism of the failure has been studied and improvements in MLC, TLC and QLC have all see rising TBW specifications.

SLC are the most durable type of cell. MLC are slightly less durable but provide double the capacity. TLC cells are less durable but are triple the SLC capacity. QLC are quadruple the SLC with even lower endurance.

All SSD are over provisioned and they use the pool of extra blocks to swap out the workout blocks. There is usually more than enough spare blocks to keep a SSD operating for many years. Wear leveling also seeks to extend the service life of an SSD array.

SSD controller logic by Psion is popular. One of the reasons is the advanced versions have RAM which can act as a fast cache to increase performance. Sandforce was popular long ago with SATA SSD but they are not widely seen with M.2 NVMe hardware.

When dynamic wear leveling is used blocks that undergo rewriting are repositioned to new blocks. The algorithm selects an empty block on which to write the data. The number of writes to each block are kept track of by the controller. A downside to dynamic leveling is that data blocks that are not frequently updated are not moved which can lead to uneven block wear.

The same techniques are employed by static wear leveling with one important difference. Blocks of static data are moved when their block erase count falls below a certain threshold. This leads to more effective leveling which results in slightly slower write performance countered with enhanced longevity of the SSD.

Given the advanced wear leveling and the sophisticated controllers the consumer does not need worry much about their M.2 SSD stuffed into a slot of their motherboard. The SSD is mature and should last for decades with typical workloads seem with gaming. Due to the architecture of the SSD its very advisable to not use more than 75% of the capacity of the unit.

Crystal Disk Reports can show the accumulated operating hours in addition to the remaining percentage of the SSD. When the SSD gets below 20% it’s wise to consider an immediate replacement. The wear on a SSD is gradual and for a typical gaming situation there is little to worry about.