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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abufrejoval - Monday, April 28, 2014 - link
I'm seen an opportunity here to clarify something that I've always wondered about:How exactly does this long time retention work for FLASH?
In the old days, when you had an SSD, you weren't very likely having it lie around, after you paid an arm and a leg for it.
These days, however, storing your most valuable data on an SSD almost seems logical, because one of my nightmares is dropping that very last backup magnetic drive, just when I'm trying to insert it after a complete loss of my primary active copy: SSD just seems so much more reliable!
And then there comes this retention figure...
So what happens when I re-insert an SSD, that has been lying around say for 9 months with those most valuable baby pics of your grown up children?
Does just powering it up mean all those flash cells with logical 1's in them will magically draw in charge like some sort of electron sponge?
Or will the drive have to go through a complete read-check/overwrite cycle depending on how near blocks have come to the electron depletion limit?
How would it know the time delta? How would I know it's finished the refresh and it's safe to put it away for another 9 months?
I have some older FusionIO 320GB MLC drives in the cupboard, that haven't been powered up for more than a year: Can I expect them to look blank?
P.S. Yes, you need an edit button and a resizable box for text entry!
Kristian Vättö - Tuesday, April 29, 2014 - link
The way NAND flash works is that electrons are injected to what is called a floating gate, which is insulated from the other parts of the transistor. As it is insulated, the electrons can't escape the floating gate and thus SSDs are able to hold the data. However, as the SSD is written to, the insulating layer will wear out, which decreases its ability to insulate the floating gate (i.e. make sure the electrons don't escape). That causes the decrease in data retention time.Figuring out the exact data retention time isn't really possible. At the maximum endurance, it should be 1 year for client drives and 3 months for enterprise drives but anything before and after is subject to several variables that the end-user don't have access to.
Solid State Brain - Tuesday, April 29, 2014 - link
Data retention depends mainly on NAND wear. It's the highest (several years - I've read 10+ years even for TLC memory though) at 0 P/E cycles and decreases with usage. By JEDEC specifications, consumer SSDs are to be considered at "end life" when the minimum retention time drops below 1 year, and that's what you should expect when reaching the P/E "limit" (which is not actually a hard limit, just a threshold based on those JEDEC-spec requirements). For enterprise drives it's 3 months. Storage temperature will also affect retention. If you store your drives in a cool place when unpowered, their retention time will be longer. By JEDEC specifications the 1 year time for consumer drives is at 30C, while the 3 months time for enterprise one is at 40C. Tidbit: manufacturers use to bake NAND memory in low temperature ovens to simulate high wear usage scenarios during tests.To be refreshed, data has to be reprogrammed again. Just powering up an SSD is not going to reset the retention time for the existing data, it's only going to make it temporarily slow down.
When powered, the SSD's internal controller keeps track of when writes occurred and reprograms old blocks as needed to make sure that data retention is maintained and consistent across all data. This is part of the wear leveling process, which usually is pretty efficient in keeping block usage consistent. However, I speculate this can happen only to a certain extent/rate. A worn drive left unpowered for a long time should preferably have its data dumped somewhere and then cloned back, to be sure that all NAND blocks have been refreshed and that their retention time has been reset to what their wear status allow.
hojnikb - Wednesday, April 23, 2014 - link
TLC is far from crap (well quality one that is). And no, TLC does not have issues holding a "charge". Jedec states a minimum of 1 year of data retention, so your statement is complete bullshit.apudapus - Wednesday, April 23, 2014 - link
TLC does have issues but the issues can be mitigated. A drive made up of TLC NAND requires much stronger ECC compared to MLC and SLC.Notmyusualid - Tuesday, April 22, 2014 - link
My SLC X25-E 64GB is still chugging along, with not so much as a hiccup.It n e v e r slows down, it 'felt' fast constantly, not matter what is going on.
In about that time I've had one failed OCZ 128GB disk (early Indullix I think), one failed Kingston V100, one failed Corsair 100GB too (model forgotten), a 160GB X25-M arrived DOA (but it's replacement is still going strong in a workstation), and late last year a failed Patriot Wildfire 240GB.
The two 840 Evo 250GB disks I have (TLC) are absolute garbage. So bad I had to remove them from the RAID0, and run them individually. When you want to over-write all the free space - you'd better have some time on your hands.
SLC for the win.
Solid State Brain - Wednesday, April 23, 2014 - link
The X25-E 64 GB actually has 80 GiB of NAND memory on its PCB. Since of these only 64 GB (-> 59.6 GiB) are available to the user, it means that about 25% of it is overprovisining area. The drive is obviously going to excel in performance consistency (at least for its time).On the other hand, the 840 250 GB EVO has less OP than the previous 840 models with TLC memory, as you have to subtract 9 GiB from the 23.17 GiB amount of unavailable space (256 GiB of physically installed NAND - 250 GB->232.83 GiB of user space) previously fully used as overprovisioning area, for the Turbowrite feature. This means that in trim-less or intensive write environments with little or no free space they're not going to be that great in performance consistency.
If you were going to use The Samsung 840 EVOs in a RAID-0 configuration you should really had at the very least to increase the OP area by setting up trimmed, unallocated space. So, it's not really that they are "absolute garbage" (as they obviously they aren't) and it's really inherently due to the TLC memory. It's your fault in that you most likely didn't take the necessary steps to use them properly with your RAID configuration.
Solid State Brain - Wednesday, April 23, 2014 - link
I meant:*...and it's NOT really inherently due to the...
TheWrongChristian - Friday, April 25, 2014 - link
> When you want to over-write all the free space - you'd better have some time on your hands.Why would you overwrite all the free space? Can't you TRIM the drives?
Any why run them in RAID0? Can't you use them as JBOD, and combine volumes?
SLC versus TLC results in a about a factor of 4 cheaper just based on a die area basis. That's why drives are MLC and TLC based, the extra storage being used to add extra spare area to make the drive more economical over the drives useful life. Your SLC x25-e, on the other hand, will probably never ever reach it's P/E limit before you discard it for a more useful, faster, bigger replacement drive. We'll probably have practical memrister based drives before the x25-e uses all it's P/E cycles.
zodiacsoulmate - Tuesday, April 22, 2014 - link
It make me think about my OCZ vector 256GB, it breaks everytime there is power lose, even hard reset...There are quite a lot people claim this problem online, and Vector 256GB became only sale refurbised before any other vector drive....
I RMAed two of them, and OCZ replaced mine with Vector 150, which seems fine now.. maybe we should add power lost test to SSDs...