Final 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.

Random & Sequential Performance
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  • Solid State Brain - Tuesday, April 22, 2014 - link

    Enterprise SSDs usually have their endurance rated at 3 months of residual data retention capability, vs 1 year for consumer models. Since data retention time decreases with NAND wear, this allows manufacturers to claim almost "for free" a higher endurance than what the P/E limit for consumer NAND memory would suggest, even though it might be the exact same memory (but different requirements).

    Most likely, the rated endurance for these drives is at a much higher number of P/E cycles than 3000.
    Reply
  • Kristian Vättö - Tuesday, April 22, 2014 - link

    "Most likely, the rated endurance for these drives is at a much higher number of P/E cycles than 3000."

    I don't think that is necessarily the case. If you look at my calculations on the "Endurance Ratings" page, the combined WLF and WAF is already only 1.24x when using the raw NAND capacity to calculate the endurance at 3,000 P/E cycles. 1.24x is excellent, so I find it hard to believe that the NAND would be rated at higher than 3,000 cycles as the combined WLF and WAF would essentially be about 1.00 in that case (which is basically impossible without compression). Also, Micron specifically said that this is a 3,000 P/E cycle part.
    Reply
  • Solid State Brain - Tuesday, April 22, 2014 - link

    As the endurance rating for enterprise drives is usually intended for a typical steady random workload (and no trim to help), the write amplification factor should be higher than the rather low value you used for your calculation. You can see that endurance figures (not just in this case, but most other other enterprise drives as well) start make more sense when actual P/E cycles for that usage/application are higher than their consumer counterparts.

    Here's a prominent example. You could try the same calculation here. In this specification sheet for 2013 Samsung enterprise drives, which includes a model with TLC NAND, it's dead obvious that the rated P/E cycles limit of consumer drives (unofficially, rated 1000 cycles) doesn't apply for them, even though for the low end models they're most certainly using the same memory. You never really see a fixed P/E cycles limit for enterprise drives as in the end is the TBW figure that counts and the shorter data retention requirement for them helps boosting that even though there might actually not be any hardware difference at all.

    http://www.samsung.com/global/business/semiconduct...
    Reply
  • apudapus - Tuesday, April 22, 2014 - link

    The specs you linked definitely show 1000 P/E cycles for all the NAND on all the drives, TLC and MLC. I used this formula: Total Bytes Written Allowed = NAND P/E cycles * Total Bytes Written per Day

    Enterprise drives have lower data retention requirements because in the enterprise space, drives will be read and written to more frequently and will not be powered off for extended periods of time. Consumer drives on the other hand can have a lots of down time.
    Reply
  • Solid State Brain - Tuesday, April 22, 2014 - link

    PM843, TLC NAND rated 1000 P/E cycles on the consumer version. Let's take the 120GB model as an example.
    Endurance with 100% sequential workloads: 207 TB

    1000 P/E (NAND life @ 1 year of data retention, on the consumer version) * 128 GiB (physical NAND capacity) = 128000 GB = 125 TiB. This drive doesn't make use of data compression. With sequential workloads the best case write amplification would therefore be 1.0x. To reach the claimed 207 TiB of terabytes written of endurance, the NAND memory on this drive would need at the very least to endure 1000/125*207 = 1656 P/E cycles, again assuming the best case write amplification factor. One can expect this to be at least around 1.15-1.20x under real world scenarios, which would bring this figure to about 1900-2000 P/E cycles.

    SM843, the enterprise version of the 840 Pro with 3000 P/E cycles MLC NAND. Again, let's take the 120GB version for reference.
    Stated endurance with 100% sequential workloads: 1 PB

    128 GiB physical capacity * 3000 P/E cycles = 375 TiB
    Actual P/E cycles needed for 1 PB at 1.0x write amplification: 3000 * 1024/375 = 8192
    Reply
  • Kristian Vättö - Wednesday, April 23, 2014 - link

    Like I said, ultimately it's impossible to figure out where exactly the endurance is coming from. It's likely that the NAND could be rated higher thanks to the looser retention requirements (3 months vs 1 year) in the enterprise space but then again, figuring out the exact P/E cycle count isn't easy because we don't know the write amplification. Reply
  • Solid State Brain - Wednesday, April 23, 2014 - link

    If you have spare time and still have the drives you could try applying a standard sustained 4kB random load for an extended period of time to figure out what the write amplification for these drives with that usage is. Marvell-based SSDs usually provide, in a way or another, both NAND writes and Host writes among their monitoring attributes, and with these data it's pretty straightforward to calculate it. Given the large OP area, I predict it will end up being somewhere around 2.5x. Reply
  • Kristian Vättö - Wednesday, April 23, 2014 - link

    I still have the drives but there are other products in the review queue. I'll see what I can do -- the process is rather simple as you outlined I've done some similar testing in the past too. Reply
  • Kristian Vättö - Wednesday, April 23, 2014 - link

    *and I've done similar testing in the past too.

    (Yes, we need an edit button)
    Reply
  • apudapus - Wednesday, April 23, 2014 - link

    OIC. My best guess is that the voltage thresholding (their ARM/OR) extends the life of the NAND. Reply

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