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Both this drive and the 980 pro have a dynamic SLC cache. When there is a significant amount of erased space available, they will each sustain about 5000MB/s. T
by mgerdts 6y ago
Both this drive and the 980 pro have a dynamic SLC cache. When there is a significant amount of erased space available, they will each sustain about 5000MB/s. This drops to about 2000MB/s as the SLC fills. The 980 pro hits a cliff at about 75% written. The SN850 requires less erased space, but I forget the exact point it cuts out.
The size of the dynamic SLC, when available, is roughly 1/3 of the erased space, with an upper bound.
If you don't need the capacity, set aside 30% of the drive in a partition you won't use, then use blkdiscard to erase it. Not only will this increase write performance, it may increase endurance. Increasing endurance with these drives is of interest because they are rated at 0.3 DWPD, compared to 1 DWPD with previous generation drives.
Taking over-provisioning to an extreme, I found that erasing a 980 Pro, then creating a 100 GB partition allowed me to overwrite that partition many times over at a sustained 5000 MB/s. This could be interesting for journaling, so long as you are ok with lack of power loss protection (unlikely for a journal) or cache flushes could be performed to ensure the data is on NAND, not just in DRAM.
But really, if you need to sustain writes at such a high rate, both of these are the wrong drive for endurance reasons. With optane stuck at PCIe gen 3, it may be great for low latency small blocks, but it won't exceed 3500 MB/s in a x4 NVMe form factor.
- ece 6y agoOver-provisioning is doable since more 15" laptops and motherboards are starting to have 2 NVMe slots, and you always could've gotten additional PCIe->NVMe slots for a motherboard. If you're still after endurance, low latency and a lot of random writes for journaling or a Bazel compiler cache, it seems like the P4801X is your best bet now, if you've got a 110mm NVMe slot.
- jlgaddis 6y ago> If you don't need the capacity, set aside 30% of the drive in a partition you won't use, then use blkdiscard to erase it. I assume this is the recommended method for over-provisioning nowadays? I've no idea where -- as it's been several years ago now -- but I can recall recommendations to use the HPA for this. I have no way to know, for certain, whether it actually helps but that's what I used to do (setting ~25% of the drive aside in the HPA). Anecdotally, I've yet to have such an SSD die on me, although I'm not exactly torturing them either.
- mgerdts 6y agoOn NVMe drives, I don't think you generally have any control over the HPA. Samsung Magician (windows only) has an option to increase over-provisioning. It shrinks the partition that is on the disk and erases the free space. Enterprise drives tend to allow namespace management. With such a drive you can delete the namespace that comes from the factory and create a smaller namespace or several smaller namespaces that have an aggregate capacity that leaves the desired over-provision space unallocated.
- ece 6y agoI hadn't looked at enterprise drives before, but the Samsung 983 DCT is affordable and available, for M.2 110mm slots. It does user over-provisioning[1] (among other Samsung drives), and is a good option for those looking for more endurance. [1] https://www.samsung.com/semiconductor/global.semi.static/S190311-SAMSUNG-Memory-Over-Provisioning-White-paper.pdf https://www.samsung.com/semiconductor/global.semi.static/S19...