With high speed comes great responsibility. Responsibility to make use of that speed wisely. So while solid-state storage can be intrinsically very, very fast, it needs a suitably quick connection to realise all that performance.

And that’s where the most common internal disk interface, second-generation SATA 3Gbit/s, is starting to show its age.

In Crucial’s last SSD, the award-winning Crucial RealSSD C300, we saw Crucial fit the then-cutting edge SATA 6Gbit/s bus to unlock its superb sequential read and write speeds. That was then; now we have even quicker drives.

Here we have a revised take on that same drive in the Crucial M4. Confusingly, it goes under two names: as well as Crucial M4, it’s also known as the Micron RealSSD C400.

The dual branding is down to the two-pronged marketing of one of the world’s major silicon fab works, Micron Technology.

It sells under the consumer names of Crucial (best identified by its extensive RAM portfolio) and Lexar Media (familiar for its USB thumbdrives), alongside its main Micron enterprise division, manufacturing DRAM and industrial solid-state storage.


When we first reviewed the Crucial C300 it excelled through its speedy Micron flash silicon, fabricated at 34nm lithography, with a generous 256MB of cache; all under the control of a clever Marvell controller chip to handle the, literally, crucial I/O traffic management and internal data supervision.

In the Crucial M4, we see the same large buffer and a near-identical Marvell 88SS9174 controller. The main change lies with the actual NAND flash, which has been shrunk to a 25nm process. And that’s how Micron/Crucial has eked out extra speed. How much more? In some respects, quite a bit more.

Lab testing

To get a good overview of the changes between C300 and C400/M4, we put the former through its paces again on our current PC benchtest workstation, before moving to the new Crucial M4 drive.

In both models, we used the 256GB capacity version.

The new headline sequential read/write speeds of the Crucial C300 as measured by ATTO Bench 32 were 348 and 238MB/s respectively. Those are quick results – but not as quick as the 438 and 281MB/s turned out by the Crucial M4.

Similar numbers unfurled in CrystalDiskMark 3.0, where the Crucial C300 showed reads at up to 356MB/s and writes at 233MB/s. Moving across to the Crucial M4, these numbers rose to 414MB/s for reads and 274MB/s for writes.

Turning the attention to the smaller file exchanges as measured by CDM, we saw a small trade in performance. For 4kB files, read speeds dropped from 33MB/s to 23MB/s between drives, while small writes rose fractionally from 89MB/s, to 90MB/s on the Crucial M4.

A similar write-centric change was observed in the 4k QD32 test (4kB at a queue depth of 32). The older drive reported reads here of 244MB/s and writes of 205MB/s – both amazingly fast results – where the newer M4 was benched at 167MB/s for reads but 244MB/s for writes.

Ins and outs

In professional server applications, the real-world performance of storage devices is often related by the number of input/output operations per second (IOPS). Here we saw some clear gains again for the Crucial M4 – particularly when multiple threads were stacked up.

The AS SSD benchmark test showed that the older Crucial C300 could notch up 7.5k and 18.3k IOPS in simple 4kB read/write transfers; rising to an impressive 56.4k and 45k IOPS in the 4k-64 thread test.

The Crucial M4 reported only around half as many read IOPS in the straightforward 4k test (3.6k versus 7.5k), while writes here were effectively the same at 18.3k versus 18.5k.

But in the 4k-64 thread test, the newer drive nearly doubled in these write characteristics, from 45k to 84k. Reads were somewhat lower though, down from 56k to 40k.

Another very fast 6Gbit/s SATA SSD that launched recently, the Plextor PX-256M2S – which hit even faster 483MB/s sequential reads in our testing – had maximum IOPS here of just 17k/11k for reads/writes.

Drive longevity is a concern for all solid-state storage; more so with the smaller die process that’s appearing. Crucial lists the M4 as able to support 2TB of writing – otherwise expressed as 40GB every day for five years.

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