Last year's Intel Haswell refresh wasn't particularly exciting because of the CPU improvements but because of the new Z97 chipset which brought SATA Express and the M.2 interface to mainstream computing. That's a big deal in the storage world and we were especially interested in M.2 (formerly 'Next Generation Form Factor' or NGFF).
It wasn't long after the Z97's arrival that Samsung moved to capitalize on the chipset's M.2 support by announcing the XP941, a PCIe 2.0 x4 SSD with top speeds of 1170MB/s reads and 930MB/s writes. To date, no other M.2 device has challenged the XP941, however as attractive as the Samsung XP941 may be, it was meant as an OEM-only product.
Nonetheless, the drive has been popular among enthusiasts -- popular enough for Samsung to announce a successor last January -- though again as an OEM product. The new SM951 PCIe SSD is currently available through Australian company RamCity, and although the drive is listed in Australian dollars on the company's website, it's selling to US customers via Amazon for $460. That seems reasonable for such a fast M.2 device.
We recently reviewed Intel's new SSD 750 Series 1.2TB, a PCI Express SSD that supports the NVMe protocol. The SSD 750 Series proved to be fast, but also expensive at $1.02 per gigabyte for the 400GB model.
NVMe support is the key feature of Intel's SSD 750 Series and it's something Samsung initially said the SM951 would have, later dropped, and just recently announced would ship as a separate revision of this drive with the same name. The SM951 we are testing today uses the AHCI command set as Samsung pushed the release of the NVMe version likely due to spotty compatibility for NVMe.
Not to worry though, if Samsung's claims are true then the lack of NVMe support shouldn't be too devastating for the SM951 as read speeds are said to reach 2150MB/s and 1500MB/s for writes, which should give the SM951 an advantage in write tests over the Intel SSD 750 1.2TB (2400MB/s and 1200MB/s reads and writes, respectively, using the NVMe driver).
Samsung SM951 in Detail
The SM951 is available in three capacities, making it more client-friendly than Intel's SSD 750 Series. Those wanting extreme speed on a budget have the 128GB model for $140, the 256GB version costs $240 and the 512GB version (what we have) costs $460, $0.89 per gigabyte.
Although the 128GB model is relatively affordable it should be noted that it doesn't have the same 1.5GB/s write performance of the 512GB model. Instead, the write performance has been cut to just 600MB/s. That makes the 256GB model much more desirable as it offers the same read performance as the 512GB model with twice the write performance of the 128GB model.
Like its predecessor, the SM951 comes in the M.2 2280 form factor, meaning any system with an 80mm long M.2 port can support this SSD. That said, users will want to make sure PCIe 3.0 is available as performance will be reduced when using PCIe 2.0, though the SM951 will still be very fast regardless.
In addition to PCI 3.0, the SM951 is the first SSD to adopt the L1.2 low power standby mode (which allows all high-speed circuits to be turned off when a PC is sleeping or in hibernation) as defined by PCI-SIG (the PCIe standards body). By embracing the L1.2 level of standby operation, the SM951's power consumption is drastically reduced – to under 2mW, about a 97% decrease from the 50mW consumed using a L1 state.
At the heart of the SM951 is the Samsung S4LN058A01 and other than the fact that this is a PCIe 3.0 x4 AHCI controller, we know very little about it.
We didn't expect to find planar 2D NAND being used on the SM951. While 3D V-NAND has done the rounds on all of Samsung's mainstream SSDs, the SM951 gets planar NAND. Found on the tiny 80mm x 22mm PCB are four 128GB Samsung 16nm MLC K9UKGY8SCD-DCK0 NAND flash chips.
Compatibility seems good and any motherboard/device supporting the M.2 interface should offer bootable support for the SM951. We tried it with a few Asrock and Gigabyte Z97/X99 motherboards and all worked perfectly.
While on the subject of compatibility, it's worth noting that like the XP941, the SM951 won't work with the Samsung Magician Software as this is an OEM product.
Because the SM951 is an OEM part, its warranty and endurance limitation are specified by the reseller instead of Samsung. The good news is sellers such as RamCity/Amazon are offering the full three-year warranty with a 72TB endurance rating, so buyers can purchase with confidence.