Review Index:

Samsung 840 EVO 500GB and 1TB Full Review - TurboWrite TLC

Subject: Storage
Manufacturer: Samsung

Write Cache Testing

We've already seen some of the effects of how the write cache interacts with our other testing. While the IOMeter results were interesting, that is a very heavy mixed workload running at high Queue Depths and is more representative of what an SSD would see in the enterprise. In a consumer environment, heavy write workloads are only typically seen during application and OS installs, and even then it is doubtful that GigaBytes of data are going to be written to the EVO at greater speeds than the cache can write back out to the TLC flash area. This only leaves sequential bulk writes to the SSD, and hitting sustained 500MB/sec writes will only take place if the user was performing a large file transfer to the EVO from either another fast SSD or from a very capable HDD RAID setup.

After dabbling with all sorts of snazzy IOMeter profiles and charts and graphs, it turned out the simplest and most repeatable demonstration came from HD Tune's write test.

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With how I had HD Tune configured, it gets just past the 100GB mark on the chart by the time it has written 12GB of data to the SSD. As a matter of fact, I timed it and it took exactly 24 seconds to get to the dip. 24*500MB = 12GB. Now to figure out how fast that cache gets completely flushed back to the TLC:

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For the above result, I aborted and re-ran the test with 10 seconds in-between. You can see the cache was not completely flushed as the EVO write speed drops to an in-between value only a couple of seconds into the write. It keeps writes as high as it can until the cache is once again completely full. Lets see what happens after a 15 seconds delay between runs:

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Then 20 seconds:

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...and finally 25 seconds:

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25 seconds was enough of a repeatable delay for the EVO to flush enough cache to disk to support another 12GB being subsequently written to it. On a few occasions I saw a full flush with only 20 seconds, and on even rarer occasions, 15 seconds. You'd figure this does not add up, as it would have to write to the TLC at greater than its (slower) sustained transfer rate. My theory is that the SLC is so fast that it can accept data at 500MB/sec and flush some of that data out at the TLC transfer rate *simultaneously*. That's some speedy TLC. That said, the EVO only appears to be this agressive if the cache has been running on the full side for quite some time. Given enough breathing room, it seems to favor filling the cache first, switching over to TLC writes once full, and emptying the cache during the next idle period.

*Note*: These tests were performed on the 1TB model. Lower capacity models are going to have differing cache sizes and TLC write speed, and will therefore alter the sustained write transfer duration prior to filling the cache and dropping to the TLC (sustained) write speed.

July 25, 2013 | 09:34 AM - Posted by Mark Strong (not verified)

Thank you for the quick review sir. Personally I would call this a no question automatic upgrade for a new PC build. I'm interested to hear your thoughts on where this stacks up in the grand scheme of things.

July 25, 2013 | 10:02 AM - Posted by Allyn Malventano

If the pricing holds (and that's a big IF since I have yet to see sub-$1/GB pricing hold), the EVO will become my default recommendation for everything but the most demanding enterprise use.

July 25, 2013 | 10:38 AM - Posted by Mark Strong (not verified)

Then let us hope with fingers crossed that the price roughly holds (within 10 - 20 dollars). Much appreciated sir.

July 25, 2013 | 11:14 AM - Posted by grommet

I didn't see in the article when these would be available- did I miss it, or are they not saying yet?

August 12, 2013 | 12:52 AM - Posted by Allyn Malventano

No hard date, but I'd imagine as quickly as they can get them out there.

July 25, 2013 | 12:44 PM - Posted by Thedarklord

Great review.

As someone who is about to jump onto the SSD train;

1)It looks like several SSD makers are releasing new products now/very soon (so is it better to wait?)

2)I personally like the Corsair lineup, anyone heard anything if they are exiting the market?, seems like their SSD market is getting scarce.

, Thanks

July 25, 2013 | 01:30 PM - Posted by Ram Rangaswamy (not verified)

Allyn Malventano: The last line of the article says "...Samsung 840 ECO..." instead of EVO.

Otherwise, love the article and insight!

July 25, 2013 | 06:01 PM - Posted by Tad (not verified)

LOL PCMO5? What the hell? and Iometer 2006? ROFLSAUCE! Its like I ran into an '80's website. Does your SSD wear parachute pants too?

July 26, 2013 | 01:23 PM - Posted by Photonboy (not verified)

If a tool works to accurately assess a product, why does it have to be made very recently?

An older product is also well understood and allows accurate comparisons to previous products that also tested with the same tools.

August 12, 2013 | 12:50 AM - Posted by Allyn Malventano

^ this.

July 29, 2013 | 11:54 AM - Posted by Moochacho (not verified)

Is there any benefit these days (performance or stability) to having one SSD for OS, another for programs and a third for data? Back in the day I used to have the OS on its own partition or even different drive, so it wouldn't get all fragged up. I currently have a 120GB OCZ Vertex3 for OS, 1TB Samsung Spinpoint for progs and 500GB WD Black for data and trying to eliminate spinning drives for new build.

July 30, 2013 | 11:06 PM - Posted by irdmoose

Hey Allyn, thanks for the great review. It looks like the bug you caught to get this review out may have been worth it, and I hope that you get well soon! How well do you think these drives will perform in a RAID-0 setup with say an Intel controller on either Ivybridge or Haswell systems?

August 12, 2013 | 12:50 AM - Posted by Allyn Malventano

They should be just fine, so long as the partition is correctly aligned (not an issue for Vista and newer). There may be a slight performance hit due to TRIM not passing through to a RAID-0 (which is still a mixed bag as far as it actually working), but it should be minimal impact for regular usage.

August 13, 2013 | 03:08 PM - Posted by jgstew

I think in the case of workloads with very little writing like a file server, the 840 EVO and similar SSDs could be an interesting replacement for something like this:

With a significantly lower $/GB and better read performance.

August 23, 2013 | 05:38 PM - Posted by klatch

Is there a concern that the flash in the turbowrite buffer is going to die early? or does it get load balanced around the drive? I was sort of expecting the buffer to actually be SLC, but if it is just making TLC operate as SLC is that functionally equivalent to it being SLC?

September 17, 2014 | 10:45 PM - Posted by Grand Nagus (not verified)

Allyn Malventano

What is the update on the 840 EVO problems?


If they don't fix the problem you should downgrade the review to Bronze or worse. :)

I bought this drive on PCPERs recommendation and now I'm pissed.

December 25, 2014 | 10:54 PM - Posted by Obat Kanker Vulva Herbal (not verified)

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