Customer Review

967 of 1,005 people found the following review helpful
4.0 out of 5 stars Good but only if you can get it at the right price, November 6, 2012
This review is from: 840 MZ-7TD500 500 GB 2.5" Internal Solid State Drive (Personal Computers)
First of all, the Samsung 840 uses triple-level cell (TLC) memory vs. the multi-level cell (MLC) memory used for almost all other SSDs. So what is the difference between TLC and MLC? With TLC memory, 3 bits of information (8 possible values) are stored per cell instead of the 2 bits (4 possible values) in MLC memory. This might sound better but it also means that the cells are used more and there is less voltage fault tolerance. In the most simple terms, you can think of cells being "filled" or "emptied" by applying voltage. When 3 bits (8 possible values) of information are stored per cell, the SSD may have to apply voltage to the entire cell multiple times even though just one bit of information is encoded (depending on the bit being changed). The multiple voltage applications to each cell also slows down the write speeds and causes more wear in general.

Performance-wise, the Samsung 840 is actually worse than the previous generation Samsung 830. On the Passmark benchmarks, it is slightly lower than the OCZ Agility 4 which uses asynchronous MLC NAND flash.

Right now, the top three SSDs (best selling and best reviews) on Amazon are the OCZ Vertex 4, Samsung 830, and the Crucial M4. However, all three of these SSDs are cheaper and they perform better than the Samsung 840. Eventually, the TLC NAND should mean that the Samsung 840 will sell for less because less NAND is used. However, it is not worth it right now. To be safe, I would say that you should wait until the drive is at least 10-20% cheaper than the three drives above due to the uncertainty of how it will perform in the long run.

One puzzling thing is that I couldn't find any mean time before failure (MTBF) estimates for the 840, while the MTBF for the 20nm MLC based 840 Pro is 1.5 million hours (lower than the 2 million hours for many 25nm MLC drives). Also, it is interesting that the drives are not 128GB, 256GB, 512GB. There are probably three reasons for this. The TLC NAND manufacturing process has lower yields so they have to "turn off" a portion of the cells to account for this. This is similar to what Nvidia does for their GPUs (16 functional streaming multiprocessors become GTX 580, 14-15 functional streaming multiprocessors become a GTX 570, etc...) Another possibility is that they anticipate that there will be more wear to the TLC NAND so that there is an unused memory bank to replace any dead cells. The third and most likely reason is a combination of the two, i.e. a portion of the turned off cells are nonfunctional due to the new manufacturing process and the remaining portion of the turned off cells are reserved for replacement.

I handle tech purchase decisions for my department and so I bought one Samsung 840 to test for due diligence but won't buy more until they become much cheaper.

-------------------------------------------------------

12/4/12 Update

As predicted, these drives dropped in price quite a bit. TLC NAND is about 25% cheaper than MLC NAND so that the price of these drives should converge to a ratio of around 75% of the price of a MLC SSD in the long run.
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Comments

Tracked by 8 customers

Sort: Oldest first | Newest first
Showing 1-10 of 35 posts in this discussion
Initial post: Nov 7, 2012 6:32:51 PM PST
Last edited by the author on Nov 8, 2012 9:13:12 PM PST
Huacanacha says:
The 840 is NOT slower than the 830 or any of the other drives you compare it against.

First point:
(note: this has now been corrected in the original review)
The possible multiple voltage applications for TLC does NOT reduce read speed. It CAN reduce sustained write speed depending on the controller and circumstances.

Second point:
Here are some of the performance numbers for the 840 vs the 830 (250/256GB drives, all numbers in MB/s)...
.......................~830~..~840~
Random read........67........84*
Random write.....161.......252*
Sequential read...409.......431*
Sequential write..364*......254
* = fastest drive

Anandtech Storage Benches 2011...
.....................~830~...~840~.~Vertex 4~.~Crucial M4~
Light (typical).....300.......335*....249..........246
Heavy...............231*......214.....222..........162

The 840 is faster than the 830 under most workloads... it's winning 3 out of 4 of the key performance metrics. System responsiveness is governed by random read/writes and maximum latencies. The edge goes to the 840 for almost all consumer and most business workloads. It's NOT suitable for servers, or for professionals with high write workloads (such as video/photo editors), but for most users the 840 will be faster.

Looking at the Storage Benches, the 840 reigns supreme for typical workloads and is still very good under extremely heavy load. I don't know how you can suggest the Vertex 4 and M4 based on performance.

It's worth noting that there are potential endurance concerns with the 840 due to utilizing TLC flash. However, unless you write a ton of data to the drive on a constant basis it shouldn't be an issue at all and overall endurance should be similar to current MLC based drives (there was a comment from Samsung about this but I'm not sure where). There are also possible issues with steady state performance, but I'd like to see more reviews focusing on this before drawing a conclusion. If you leave at least 20% of the drive free you give yourself a better chance of maintaining good performance.

Conclusions:
I do actually agree with your main point: If the other drives are cheaper they're a better deal. By far the most noticeable improvement is moving to an SSD from a Hard Drive. The difference between a fast and very fast SSD can be subtle.

For most people I suggest evaluating an SSD purchase on the following criteria:
1) Has good to very good performance
2) Has proven reliability... 830: yes, M4: yes I think, Vertex 4: maybe (OCZ have had many issues), 840: not yet (too new)
3) Given 1) and 2)... as large a drive as possible within your budget

For people wanting the absolute best performance the Samsung 840 Pro blows the current competition out of the water. It's also a new drive, but it's using more proven MLC flash and Samsung have been amongst the most reliable SSD makers. It will cost you a pretty penny though!

Source:
http://www.anandtech.com/show/6337/samsung-ssd-840-250gb-review (pages 6, 9, 10, 11)

Edit: changed/removed some of the wording after the original review was corrected. Thanks!

Posted on Nov 7, 2012 8:35:32 PM PST
Technologist says:
I did have a typo on the read speed slowdown and it has been fixed. However, I stand by what I said. Every benchmark will give somewhat different results and it can be difficult to ascertain which is the most relevant. I would argue is quite idiosyncratic. My main point is that the Samsung 840 is not worth it right now given that it is more expensive than the three drives I listed (especially when they are on sale which seems to alternate week by week).

Storage review has provided probably the most comprehensive review of the Samsung 840 Pro and even it is not a clear winner, http://www.storagereview.com/samsung_ssd_840_pro_review

It does some things better and some things worse than the other fourth generation drives.

Posted on Nov 8, 2012 8:38:34 AM PST
Vishnu says:
Thanks for your review..i was going to buy ssd 840 but now i changed to 830..

Posted on Nov 8, 2012 1:58:03 PM PST
Dan says:
"Good but not at this price" - What price did you pay for the 840 500GB?

In reply to an earlier post on Nov 8, 2012 3:14:52 PM PST
Technologist says:
I didn't buy the 500GB, I wrote the review for the "wrong" model but fortunately Amazon aggregates it. Paid $115 for the 120GB which is no good considering you can find the other three I talk about for $90 or below.

In reply to an earlier post on Nov 8, 2012 6:55:16 PM PST
Last edited by the author on Nov 18, 2012 1:14:09 AM PST
Huacanacha says:
Thanks for making that correction, I've updated my original comment to reflect this. The 840 Pro review you linked is interesting... I'd certainly agree that there are many facets to SSD performance, and the absolute best drive will depend on your use-case (if you can even define it that well!). However, I do like the Anandtech storage benches because they use actual IO's recorded for two fairly realistic usage scenarios, rather than simulated test patterns or synthetic benchmarks. Both the Light and Heavy benches are for consumer/professional workloads though, and clearly the server oriented benchmarks don't favor any one drive in all cases.

In general I would like to see SSD reviews cover the maximum read/write latencies more, as well as the performance of the drives when new vs near full vs steady state, as these metrics are key to understanding the true performance people can expect to see. I know the Agility 4 (and possibly the Vertex 4) perform much worse by design as the drive fills up. It does seem that OCZ have vastly improved these drives with firmware updates which is great to see, so maybe it's not such an issue now.

We definitely agree on the main point:
*** Buy the drive that gives you the best bang for buck! ***

The top drives all perform at a similar level... most people would be hard pressed to tell them apart. They should all be up for consideration after factoring in current pricing and reliability.

--

Edit: I found some additional helpful reviews to cover some of the issues discussed above. Unfortunately the Samsung 840 and 840 Pro aren't included, but you can see the importance of steady state and full/part full drive performance.

HardOCP (steady state, latency) - http://www.hardocp.com/article/2012/10/24/plextor_m5_pro_ssd_review/5
HardwareCanucks (full drive performance) - http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/57398-corsair-neutron-240gb-neutron-gtx-240gb-ssds-review-11.html
XBit (steady state) - http://www.xbitlabs.com/articles/storage/display/plextor-m5-pro-m5s_6.html#sect0
Tech Report (latency, used state) - http://techreport.com/review/23887/samsung-840-series-ssd-reviewed

In reply to an earlier post on Nov 9, 2012 10:03:49 AM PST
Technologist says:
I'm glad we could come to some sort of agreement Huacanacha. I updated my review to point to the comment section for more in depth technical discussion.

I am of the opinion that every consumer should have a SSD for their main operating system drive nowadays. It is by far the best upgrade you can make to a PC. A SSD in any quad core processor (post Intel Core 2) would probably "feel" faster than the best processor with a standard hard drive.

One other thing I would like to add about the 840 is that reliability is an unknown at this point. I suspect that it will be mostly fine but I'm going to play devil's advocate for a bit.

One puzzling thing is that I couldn't find any MTBF estimates for the 840, while the MTBF for the 20nm MLC based 840 Pro is 1.5 million hours (lower than the 2 million hours for many 25nm MLC drives). Also, it is interesting that the drives are not 128gb, 256gb, 512gb. There are probably three reasons for this. The TLC NAND manufacturing process has lower yields so they have to "turn off" a portion of the cells to account for this. This is similar to what Nvidia does for their GPUs (16 functional streaming multiprocessors become GTX 580, 14-15 functional streaming multiprocessors become a GTX 570, etc...) Another possibility is that they anticipate that there will be more wear to the TLC NAND so that there will be a unused memory bank to replace any dead cells. The third and most likely reason is a combination of the two, i.e. a small portion of the turned off cells are nonfunctional due to the new manufacturing process and the remaining portion of the turned off cells are reserved for replacement.

Finally, BTW I have a Vertex 4 which I like very much. The IOPS are crazy and almost all of the negative reviews were before firmware version 1.5 came out.

Posted on Nov 11, 2012 5:49:35 PM PST
Lee Thompson says:
Think you meant 2 bits vs 3 bits. 3 bits gets you integer values from 0 to 7. 2 bits gets you integer values from 0 to 3.

In reply to an earlier post on Nov 11, 2012 7:28:54 PM PST
Technologist says:
Yeah my bad. I meant 8 vs. 4 possible values.

In reply to an earlier post on Nov 16, 2012 5:36:03 PM PST
J. Graham says:
Another good review of the 840 series (not the pro) has recently been posted on TechReport. It gives a good cost/value comparison of several of the most popular SSDs.

http://techreport.com/review/23887/samsung-840-series-ssd-reviewed
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