The large SSD memory test

Two exquisite SSDs compete against each other in this duel. The current top model ADATA XPG SX910, will be challenged by the brand new Plextor M5 Pro, which will be available from mid-September. At first glance, the duelists look very much like each other. Both SSDs have a capacity of 256 GB, both cost around 260 € and the manufacturer’s read speeds are about the same high level – at 540 and 550 MB / s respectively.


Tasks of the controller


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Performance data and laboratory values ​​


By the way, "XPG" stands for "extreme performance gear" at ADATA, which is supposed to mean "exceptional performance". The ADATA is powered by the current SandForce SF-2281 controller, which is also used in many other solid-state disks.


Conclusion


The new M5 Pro from Plextor is powered by a 88SS9187 controller from Marvell. Marvell does not serve as many SSD manufacturers with their controllers as SandForce. However, this does not mean that these make worse work. The controller does not only depend on maximum transfer rates. It is also responsible for fast access and other tasks.


The controller has control over all data. It accepts requests from the operating system and causes access to corresponding data blocks. Of course, the quality and speed of the memory used also plays a role in the data rate. In principle, however, the following can be said: the faster queries are processed, the faster the data transfer. SSDs also play an important role in storage management, which is also dependent on the quality of the programmed firmware.


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For SSDs, data such as HDDs can not be easily overwritten. The deletion process is a more complex matter. Data can only be deleted in so-called blocks. A block consists either of 128 so-called "Pages" with 4 KiB, ie 512 KiB, or from 256 pages with 8 KiB each, ie 2 MiB. These deletions are called PE cycles (program erase). In this case, the memory cells are completely flooded with electrons - in quite a rabid manner. Unfortunately, each PE cycle leads to the wear of the "tunnel oxides", a material responsible for charge conservation.


A single storage cell of a consumer SSD now allows about 300 PE cycles before it can be described with new information. This is why the controller also has important tasks such as the uniform description of the memory (wear levelling). In terms of service life, an SSD controller must ensure a perfect balance: the write speed is only high if there are empty memory blocks. However, since deletion is limited, half-full blocks should not be deleted.


The XPG SX910 achieves enormously high maximum transfer rates. The maximum read rate of 554 MB / s is very impressive and the same is true for the maximum write rate of over 500 MB / s. Especially at the maximum write rate the Plextor M5 Pro pulls the shorter stalk, because it comes only to almost 453 MByte / s. The secret of the SX910 is the SandForce controller. This is able to compress data before sending it.


This advantage, however, only comes to full advantage in files that are at least one MByte in size. The smaller the data to be transported, the less effective is the compression. For example, the Plextor M5 Pro reaches 52.9 MByte / s with 1 KBytes of data, the XPG SX910 kicks in at only 32.3 MByte / s. It is obvious that data that is compressed already moved by the SandForce controller is slower.


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The fact that the trick with compression does not pay off for all requirements is also evident in the sequential data transfer. If the controller continuously writes data to the flash memory, the Adata reaches almost 300 MB / s in our laboratory. The Plextor is significantly faster with 401 MB / s. For project work with video files, which are then rendered, the Plextor would be more suitable. For example, if you often edit photos and load them into a software, Adata has some advantages.


However, the difference is the IOPS (input-output operations per second). We measure the IOPS for different file sizes. It shows a similar picture as with the writers and readers for different file sizes. The smaller the data, the more clearly the differences between the Plextor with Marvell controllers and the Adata with SandForce controllers. For 512-byte files, the Plextor hits the Adats almost crushing. You'll also have a huge amount of memory access time.


Both products are very similar in terms of price, size and equipment - but the difference is significant. The Plextor with Marvell controller is ideally suited as a system disk with its fast access time and the fast transfer rates for smaller files. The Adata with its top performance at maximum transfer rates, however, is more for photographers who have a lot of image processing to do.


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