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–°rucial M550: New Version of Old Platform

The first thing we should note about the M550 series is that it’s not a replacement for the M500 but adds to the latter from above, being somewhat more expensive yet still very attractive for price-conscious buyers. The old M500 will be substituted by the MX100, which is another new SSD from Crucial, but we’re going to cover it in a different review.

As for the Crucial M550, it is as extensive a series as its predecessor including SSDs that range in capacity from 128 gigabytes to 1 terabyte and are available in multiple form-factors (2.5-inch desktop, mSATA and M.2). Each version uses the SATA 6 Gbit/s interface. The 1TB model is only available as a traditional 2.5-inch desktop drive.

In our review we will focus on the 2.5-inch form-factor which is represented by the following models:

These models come at recommended prices of $0.75 to $0.5 per 1 gigabyte, larger-capacity models having a lower per-gigabyte price.

Each M550 model uses 20nm MLC NAND flash memory from Micron. As opposed to the M500 which has 20nm memory with 128-gigabit (16-gigabyte) dies, the M550 only has such memory in its 512GB and 1TB versions whereas the 128GB and 256GB versions come with 20nm MLC memory in traditional 64-gigabit (8-gigabyte) dies. This differentiation increases the number of chips in the junior versions so that the SSD controller could use parallel data access more efficiently. The 256 and 512GB versions of the M550 drive have the same level of memory access interleave, which results in nearly identical performance. It is only the 128GB version that has lower performance, just as expected from a junior, low-capacity model.

One more difference of the M550 from the M500 series is a minor increase in storage capacity. It used to be a multiple of 120 gigabytes but now it is a multiple of 128 gigabytes. The additional 6.7% of storage space is taken from the RAIN technology thanks to optimizations in the drive’s internal operating algorithms.

RAIN (Redundant Array of Independent NAND) is Crucial’s exclusive RAID-like technology that provides additional data integrity protection. With RAIN, all data on the SSD is accompanied with checksums. In the M500 series, there was 1 checksum byte per each 15 bytes of data to monitor read/write errors and recover data from defective MLC NAND memory cells. The technology made sense because the M500 series came out in April 2013 with Micron’s then-new 20nm flash memory which might have stability issues. The checksums would ensure increased reliability for the M500 drive and even let it survive a complete failure of one MLC NAND chip.

Now that the 20nm tech process has matured, the quality of Micron’s MLC NAND chips is much higher, so there is no need for such measures. The RAIN technology in the M550 series uses fewer checksums: 1 checksum byte per each 127 bytes of user data. In other words, the 256GB version of the drive only allots 2 GB for RAIN. The rest of the inaccessible storage space (15.5 GB) is required for garbage collection and wear levelling techniques. The same proportion is preserved in the versions with other capacities.

Notwithstanding the changes in the RAID implementation, reliability remains in the focus of Crucial engineers, so the M550 borrows all the hardware solutions that used to make the M500 more reliable. Particularly, each model in the M550 series has capacitors that let the controller complete all data operations in case of a power failure. The new drives also feature temperature protection: if the SSD overheats, the firmware lowers its controller clock rate until the temperature gets back to normal.

Besides the different flash memory configuration, the Crucial M550 features the newer Marvell 88SS9189 controller. Although the manufacturer says it is hardly different from the M500’s 88SS9187 controller, the new SSDs are specified to be considerably faster than their predecessors even if we compare large-capacity models with 128-gigabit MLC NAND flash memory. Crucial explains this by referring to significant firmware optimizations but doesn’t reveal any details.

Like the M500, the M550 series supports AES-256 hardware encryption which can be managed from the OS environment. The new SSDs comply with the Microsoft eDrive specification, so their hardware AES engine can be enabled via the standard BitLocker tool.

New in the M550 series, the DevSleep power-saving mode is supported. It is used in Windows 8 in the connected standby state. The manufacturer says the power draw is lowered to a few milliwatts in this case whereas in the ordinary idle mode the SSD requires about 150 milliwatts.

 
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