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Samsung 840 Pro SSD – Revisited

Posted 27 February 2014 18:40 CET by Wendy Robertson

Not that long ago, Samsung acquired a software company 'NVELO' who specialise in SSD caching software. At the time, I and many others were rather puzzled why Samsung made this acquisition. Well, now it becomes clear.

Samsung's Magician software (4.3) supports 'Rapid' mode on selected Samsung SSDs, currently the 840 EVO, 840 EVO mSATA models, and also the 840 Pro. Only one SSD in the system can run in 'Rapid' mode, regardless of how many qualified SSDs are installed.

Basically what 'Rapid' mode does is use system RAM as a cache, where regularly used applications and data are stored in Rapid's cache. Since system RAM is very much faster than NAND, a huge boost in performance can be gained. This is especially true for small random files at low queue depths.

Rapid mode uses a filter driver which monitors the file systems I/O activity, and will intelligently cache the data that the user accesses most frequently. Up to 25% or a maximum of 1GB of system RAM will be used for "Rapid's" cache.

I decided to run some tests, comparing 'Rapid' mode with normal mode, and will present the results below by simply showing screenshots of the two modes. In each test I will first show the result of 'Rapid' mode, then follow that with the result obtained in normal mode.

AS SSD

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

As we can see, writing speeds especially have risen by a huge margin, random and sequential reading speeds have also received a large boost.

Anvil's storage utilities (100% Incompressible)

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

Once again, we can see a massive boost in writing performance, with an incredible 706K IOPS witnessed for 4K random writes at a queue depth of 16. Reading speeds are also up, but by a more modest margin.

IOMeter 4K random write (QD1)

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

Once again we can see a massive boost in performance, with 4K random writes up from 136.05 MB/s to 545.19 MB/s.

IOMeter 4K random read (QD1)

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

This time there is a small decrease in performance.

IOMeter sequential write (QD1)

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

Low queue depth sequential writes receive a large boost in performance, up from 508.27 MB/s to 713.90 MB/s.

IOMeter sequential read (QD1)

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

This time we see a slight decrease in performance.

PC Mark 8

To see what would happen with a real world scenario, I also ran PC Mark 8 HDD suite in Rapid mode.

Samsung 840 Pro 256GB - Rapid mode

Samsung 840 Pro 256GB - Normal mode

The 'storage bandwidth' score has risen substantially in 'Rapid mode'.

Summary

As we have seen from these tests, there is a large boost in performance to be had from running in 'Rapid mode', at least with synthetic benchmarks. So how will this translate into the real world?

Time did not allow for an extensive study into real world performance with 'Rapid mode' enabled. For the short time I did have Rapid mode enabled on the 840 Pro 256GB SSD, there was the feeling of the system being more responsive, but this is difficult to quantify. The PC Mark 8 score did rise, but not by a huge margin, although bandwidth did increase by quite a large amount.

One thing that is clear is, as the Rapid mode driver matures, it gets faster with each new version. The version that is installed with Magician 4.3 is a good deal faster than the beta version that was available when I tested the SATA version of the 840 Pro.

So what is the downside of using Rapid mode?

I would say that before you even contemplate using 'Rapid mode', you should ensure that your system is 100% stable. As you're going to have your data in a RAM cache for a time before it's permanently committed to NAND, a system crash, or for that matter a power outage, could result in data loss.

Having said that, my system is very stable, and I have been running in Rapid mode since September 2013 on the 840 EVO 750GB SSD, and have not come across a single issue with Rapid mode whatsoever.

 

Now let’s head to the next page, and see how well the drive performs after heavy use....

 

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