Micron M500DC (480GB & 800GB) Review
by Kristian Vättö on April 22, 2014 2:35 PM ESTFinal Words
Overall the M500DC is a sensible addition to Micron's enterprise SSD lineup. It fills the gap between the consumer M500 and the P400m by providing a solution that is affordable yet has the feature set and meets the performance requirements of enterprise customers. The performance is actually far better than I expected from an entry-level drive, although I must admit that I was surprised (and perhaps a little terrified too) when I noticed that Micron sets aside up to 42% (!) of the NAND for over-provisioning and RAIN. While this isn't anything new for Micron (45% of the NAND in the P400m is inaccessible to the user), it's certainly a lot given that most of the competitors are only setting aside 27% or 12% of the NAND.
I think this is also where Micron's strength culminates. While using every possible bit in the NAND is crucial for the fab-less competitors to cut costs, Micron can use a bit more NAND for over-provisioning while remaining competitive in price as the NAND is so much cheaper for them. That also helps with the R&D costs because unlike Intel and many others, Micron isn't designing their own controller but relies on Marvell for the silicon.
| Micron M500DC | Intel SSD DC S3500 | |
| 120GB | $220 | $159 |
| 240GB | $366 | $275 |
| 480GB | $609 | $543 |
| 800GB | $1006 | $886 |
Pricing in the enterprise space behaves a bit differently than in the client world. As drives are generally purchased in bulk, Micron couldn't provide any specific MSRPs for the drives, hence I had to rely on one of their resellers. The above table uses Arrow's pricing to give some idea of the typical cost. The Intel S3500 prices are Intel's bulk prices listed on their site but I'd like to emphasize that the prices here may not be very accurate and potential buyers should consult their distributors before making any purchasing decisions.
Update: Micron just sent us a note that one of their other resellers, CDW, sells the M500DC at noticeably lower prices, so I've updated the pricing table with the new prices. CDW also carries the S3500 and I've included its retail price in the table as well. Still, customers buying straight from Micron should expect even lower pricing as these single unit prices.
The M500DC carries a small premium over the S3500, but then it often performs substantially better as well. Most of the difference is due to the amount of NAND Micron sets aside for over-provisioning and NAND because that NAND is still a part of the bill of materials. If we compare the price against the total amount of NAND onboard, the pricing of the M500DC doesn't look that bad ($0.79/GiB vs $1.06/GiB for the S3500 at 480GB). I'm still not convinced that setting aside that much NAND is the best solution but it's understandable when seeking maximum performance and reliability for enterprise workloads. As the NAND lithographies get smaller, the increasing over-provisioning is the trade off that has to be made in order to avoid impacts on performance and endurance.
Ultimately, there is no one drive that is the best in all aspects and it's up to one's workload to find out the most suitable drive. I believe the M500DC provides a well balanced solution for the hyperscale customers that require consistent performance but are not looking for extreme endurance. The hyperscale market is quickly growing and will continue to do so and more affordable enterprise SSDs with regular MLC will continue to aid that growth.
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apudapus - Tuesday, April 22, 2014 - link
I don't quite understand your statement in the first part:data retention decreases with NAND wear -> consumer drives have higher endurance
Regarding the last sentence, SSD endurance is measured in number of writes like TBW. NAND endurance is measured in P/E cycles. The endurance of an SSD should not be measured in P/E cycles because erasing is handled internally to the SSD, there is no "erase" command to send to an SSD (trim does not directly yield an erase), write amplification (decreases endurance) and overprovisioning (increases endurance) must be taken into account and is not controlled by the user. Total writes is all that is needed when discussing SSD endurance. With that said, please explain your reasoning for the drive having a higher endurance than 3000 "P/E cycles".
Solid State Brain - Tuesday, April 22, 2014 - link
The more P/E cycles your NAND memory goes through, the shorter its data retention time gets.Therefore, the shorter the data retention requirement for the intended usage is, the more P/E cycles you can make your memory can go through (or in other words: the more data you can write). Actually it's a bit more complex than that (for example the uncorrectable bit error rate also goes up with wear), but that's pretty much it.
apudapus - Wednesday, April 23, 2014 - link
I see. So the assumption is that NAND with shorter data retention requires more refreshing (a.k.a. wasted programs). I believe this to be true for enterprise drives but I would be surprised to see this being done on consumer drives (maybe for TLC, though).valnar - Tuesday, April 22, 2014 - link
I wish they would find a way to lower the cost of SLC. Look at those endurance numbers.hojnikb - Tuesday, April 22, 2014 - link
Why would you want SLC anyway ?If you need endurance, HE-MLC is plety enough.
Unless you write like crazy; them probobly buying SLC shouldn't pose a problem :)
valnar - Tuesday, April 22, 2014 - link
Because 20nm TLC and crap like that barely holds a "charge", so to speak, when not powered up. That's just way too volatile for my liking. I'm not always running all my PC's every day.bji - Tuesday, April 22, 2014 - link
What difference does it make if the drive is powered up or not? These are static cells, they are not "refreshed" like DRAM. They are only refreshed when they are rewritten, and if your drive is not doing continuous writes, it's not guaranteed to rewrite any particular cell within any specific timeframe.apudapus - Tuesday, April 22, 2014 - link
NAND has limited data retention and should be refreshed like DRAM, albeit at a much larger timescale like 1 month (TLC) to a year (I believe 54nm SLC from years ago had this spec near the end of its life, ~100,000 P/E cycles). Good SSDs should be doing this.Kristian Vättö - Wednesday, April 23, 2014 - link
ALL consumer drives have a minimum data retention of one year, regardless of the type of NAND (SLC, MLC or TLC). This is a standard set by JEDEC. For enterprise drives it's three months.apudapus - Wednesday, April 23, 2014 - link
That may be the requirement for drives but not for NAND. Drives can do several things to increase data retention: refresh stale data after time, provide strong ECC, do voltage thresholding, etc. I think JEDEC specifies hundreds of hours for NAND retention.