AData Premier SP550 240GB SSD Review
The SSD segment has seen a good amount of contraction over the last two years and that trend has continued as of late. With drive technology hitting the limits of SATA 6Gbps, SATA Express being treated like a leper by most companies and the expensive NVMe just starting to make inroads, some may even say the mainstream and slightly higher end segments are experiencing a bit of stagnation. This has actually led to a bit of a renaissance within more affordable price brackets where buyers can now combine very aggressive SSD cost with capacity and a good amount of performance as well.
AData has taken the present state of the SSD market in stride by putting a focus upon delivering that optimal blend of features and pricing which buyers are now accustomed to looking for. A little while ago we looked at the first phase of their multi-pronged approach: the XPG SX930. That drive featured excellent NAND, very good performance and backed it up with a unique controller solution. Unfortunately we found it a bit expensive in comparison to some of its competitors like Crucial’s excellent MX200.
With the XPG SX930 being a tad on the costly side, we’re now turning to AData’s more affordable alternative. Called the Premier SP550, this SSD isn’t a direct upgrade from the older SP500 series per se but it does reach some impressively low $ / capacity numbers. To be precise the 240GB version of the SP550 has on online asking price of only about $80USD. For budget minded consumers who may have never owned an SSD this price point is a lot more palatable than the XPG SX930's $105. In fact the SP550 is priced $10 less than OCZ's entry level Trion 100. Meanwhile, on paper at least, it offers some pretty robust performance figures.
Naturally, in order to offer a much less costly solution for buyers AData had to make some sacrifices. These certainly don’t negatively affect its throughput but they could have more subliminal impacts.
The first and arguably largest difference between this and other AData SSDs is the NAND. Instead of using highly binned "enterprise grade" MLC+ NAND ICs, AData has instead gone in a completely different direction and used TLC NAND ICs. TLC certainly doesn’t have the extreme endurance, data retention capabilities or performance of some other NAND types. However, it is inexpensive to source and offers more than enough durability for years of running within a home-use environment. This makes it absolutely perfect for the SP550.
Interestingly, like many of their competitors, AData has chosen a Silicon Motion controller for this budget-friendly drive but in this case it is the newer SM2256 version. When compared directly to the 2246EN found in Crucial’s BX100 series, it has a revised 4-channel layout and numerous built in features to ensure that the TLC NAND it is paired with will last well past the point the drive becomes obsolete.
To do this SMI has configured the NAND ICs into a RAID type array which gives the SP550 an extra layer of ECC. While not the first to arrange the NAND into a 'RAIN' or "RAISE" array this extra ECC - or what SMI calls a "Low Density Parity Check ECC" - reduces concerns over data corruption. It may not eliminate it since static data stored on TLC does corrupt faster than on MLC, but more ECC means longer periods of time before it becomes uncorrectable.
They controller and its DPC abilities are only the first half of the equation, and much like the MX200 and Samsung Evo series, this drive uses a portion of its NAND in quasi-SLC cache mode. Unfortunately it is hard set at a rather piddling amount instead of being flexible like within Crucial’s drives, but this makes the NAND much more durable since only long term writes are written to the “fragile” TLC NAND portion of the drive.
It is this combination of increased ECC and enhanced durability that allows the SP550 to boast a 90TB of Total Bytes Written (over only 3 years) for the 240GB version. This is noticeably better than the Crucial BX100 series and well in excess of what home consumers will actually need. In other words, instead of worries over the NAND, the only major concern is performance.
Opening up the drive we can see that AData has opted for a smaller PCB, but is still capable of handling 16 NAND ICs, the SMI controller, and two DDR3 Ram ICs.
Unfortunately, much like ONFi 3 MLC NAND which are also has a 128Gbit density, these 128Gbit TLC NAND IC need a lot fewer layers in order to hit a given capacity point. Hence why AData’s 240GB model only has 8 of the 16 locations populated with TLC NAND ICs and the number of layers per IC is rather mediocre at 2. This will negatively impact short and long term performance as it the NAND interleaving (the number of NAND layers per channel) that makes a drive “fast”.
AData has also opted to only populate one of the two RAM locations. Specifically this model comes with one DDR3-1600 256MB module for caching purposes, though based on previous experience with SMI controllers this should prove more than adequate.
AData has not used Crucial, Toshiba or Samsung TLC NAND ICs. Instead they have opted for the lesser known SK Hynix TLC NAND ICs. These 128Gbit (32GB) NAND modules aren’t used all that much, but given the fact that SMI have a strategic partnership with SK Hynix the controller should be able to fully harness them.
In order to further reduce cost, there’s also a lack of onboard capacitors or other means of providing short term power in the event of an unexpected power failure. This in conjunction with the fact that a portion of the NAND is set aside for 'caching' purposes means the chances of data corruption happening from a power failure are greater than they are on an 'old fashioned' SSD like the XPG SX930.
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