SSD Endurance
The fastest plot creation is done completely in memory, but requires a server with a large amount of DRAM (256 GB for BladeBit CUDA, or 416 GB for BladeBit RAM). Most consumer motherboards don't support this much memory, so temporary storage must be used. This typically comes in the form of an SSD.
Mainstream SSDs today use NAND flash technology to store data. NAND is high performance, scalable, and low cost - warranting the use in virtually every computing segment from mobile phones, SD cards, consumer laptops, and data centers. However, NAND must be erased before the cell is programmed, a process known as a program erase cycle. This can only be performed a certain amount of times before the NAND cell wears out and can no longer reliably store user data. This is defined generally as an SSD no longer meeting the UBER (uncorrectable bit error rate), retention time (how long the device can store user data safely while powered off, at a given temperature), or functional failure (device can no longer power on).
![TBW versus DWPD](/img/ssd-endurance/tbw_dwpd.png)
The metrics to measure endurance of an SSD is defined in Terabytes Written, or TBW, at a certain workload. The workload defined is generally the JESD219 workload from JEDEC organization. An SSD can still plot well beyond meeting its rated TBW limit, because UBER can be measured (when seeing host errors) and retention is not required (Chia plotting requires temporary or ephemeral storage).
Plotter | Cache / Ramdisk | Writes per K=32 |
---|---|---|
Chiapos beta (2020) | 0 | 1.8 TBW |
Chiapos 2021 | 0 | 1.4 TBW |
madMAx Chia_plot | 0 | 1.43 TBW |
madMAx Chia_plot | 110G | 0.396 TBW |
Bladebit Disk | 0 | 1.225 TBW |
Bladebit Disk | >99G | 0.381 TBW |
Consumer NVMe SSDs are generally not recommended due to their lower endurance, and they often employ caching algorithms to faster media (SLC, or single level cell) for great bursty performance. They do not perform well under heavy workload sustained I/O. There are very high performance consumer NVMe SSDs that will offer great plotting performance, but the lower rated endurance in TBW will result in a faster wearout.
Here are some endurance examples.
You can learn more about SSD endurance from this SNIA whitepaper from JM.