NVMe: Explained

NVM Express or NVMe is a specification for accessing solid-state drives, attached through the PCIe bus. NVM stands for non-volatile memory, which is used in SSDs. It was designed from ground up, capitalizing on low latency and high performance.

Up until now, SSDs were mostly using SATA or SAS for interfacing with the rest of the computer. Since they became faster by the day, the SATA standard was saturated pretty fast and so the PCIe SSDs were born. The first generations introduced speeds of over 1 GB per second, which was more than the double of a SATA SSD.

NVMe is not a new technology by any stretch of the Imagination. The works started in the second half of 2009, and the first public release was in Q1 2011, but there weren`t any drives until July 2013 when Samsung made the move to create a drive that supported 3GB/s read speeds.

The thing that makes NVMe so fast is that it used four lanes of PCI Express 2.0. I say made, because Intel came up to the table couple of days ago with an NVMe drive that used PCI Express 3.0, that resulted in an effective speed doubling on supported devices.

Speed is not everything with NVMe. Lattency is also a big thing. Having such low latency between transfers, means that not only the large files will move fast, but also small files that were always a headache to move from a drive to another due to latency problems.

  AHCI NVMe
Maximum queue depth 1 command queue;
32 commands per queue
65536 queues;
65536 commands per queue
Uncacheable register accesses
(2000 cycles each)
6 per non-queued command;
9 per queued command
2 per command
MSI-X
and interrupt steering
single interrupt;
no steering
2048 MSI-X interrupts
Parallelism
and multiple threads
requires synchronization lock
to issue a command
no locking
Efficiency
for 4 KB commands
command parameters require
two serialized host DRAM fetches
gets command parameters
in one 64 Bytes fetch

 

NVMe is basically the old AHCI protocol on steroids. From the table above we can understand that NVMe is way more powerful than AHCI. This is achieved by its ability to exploit parallelism in host hardware and software, manifested by differences in depth of command queues, interrupts processing, the number of uncacheable register accesses etc.

If you are thinking that there is a catch to this, then … you are right. The price is so high at the moment that it`s not worth it, but in couple of months prices will come down in price.

In conclusion, NVMe is the future of storage with low latency and high access speeds and basically all around nice features.

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BMC

My name is BMC and I am a superhero. Well, maybe not a superhero, but what is certain is that I am an aspiring writer with high hopes and big dreams. I started writing in the summer of 2013 on this website and let me say, it is a fantastic ride!

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