OSDev.org

SCSI was once the hot thing and a strong competitor to IDE/ATA. Nowadays SCSI has disappeared completely.

What happened?

Regards
Peter

Hi Peter,
SCSI is more expensive and is a complex standard. It is typically used in Enterprise hardware ( think HP, Dell etc). It is still active, but not as much in the consumer world. The recent trend is to use inexpensive hardware and to implement reliability in upper software layers. This implies SCSI standard might die a slow death.

--Thomas

ATA got faster. Once you could get the same speed at a lower price than SCSI, there was no reason to use SCSI in consumer devices.

The story is a bit different in the enterprise world, where SCSI is the most popular protocol for storage area networks.

SCSI drives do still exist, in the form of SAS, but I don't think they're all that popular. I wonder if NVMe will be enough to end SCSI as a protocol for individual drives.

USB mass storage uses SCSI as a protocol.

if i remember correctly, SCSI can daisy chain several drives which was main advantage of IDE. I think they use same protocol?

Nowadays imo, both IDE, SCSI wont cut it.
With powerfull I5-8400 + 32GB RAM, my desktop window takes forever to boot and login and finish loading startup programs with IDE 5200RPM.
Latest virtual game HALF LIFE Alyx virtual reality takes forever to load between game chapters. The game size is 60GB.
I think IDE 5200RPM average about 200M/sec.

I am tired of waiting forever and purchased recently 1GB NVME PCIe drive which removes SCSI protocol cmopletely and uses NVMe protocol directly over PCIe bus (no adapters, no cables) and transfers at least 4-5 faster than my IDE and situation resolved quickly.

I forgot about that! The USB 3 standard introduced USB-attached SCSI, which means USB hard drive enclosures now use SCSI. (The drives inside the enclosures are typically SATA though.)


No, SCSI and ATA are not the same protocol.


It's fast because it's a SSD, not because it's NVMe. SCSI over PCIe would be similarly fast.

[/quote]

Hmm I am not sure about that. It should be due to its protocol NVMe specially designed for fast NVME drive.
You are right that NVMe are SSD based and SSD is faster than ATA/SCSI drives but still if it is used over IDE/SCSI busses, it will slower due to bottleneck.

https://www.networkworld.com/article/32 ... bottleneck.

I aint storage expert quick research shows:
SAS max speed: 6Gb/S ~ 480MB/s?
PCIe 3.0/4.0 speed: 8GT/s, 16GT/s respectively, depending on bit rate and lane numbers, with approx 1GB/sec per lane, and considering usual 4 lane for PCIe drives, could reach 4G/s. For pcie4.0 it is 16GT/s.
It appears M.2 can integrate PCIe as well as other busses, so up to 4 lanes so similar as PCIe.

I think this thread is getting a bit murky. I thought I will clarify a bit.
ATA,SCSI etc are standards. There are different revisions and addendum to these standards. Their implementation can take different forms.


There is nothing stopping you from implementing the standard on an HDD. It would be incorrect to say that a standard relies on implementation. It would be fair to say that the usual implementation of NVMe is on SSD storage.

--Thomas

No, you'll see the same bandwidth over PCIe whether your drive is NVMe or SCSIe ("SCSI Express"). The advantage NVMe has over SCSI is a much deeper command queue, so software doesn't have to interact with the drive as often in order to reach that peak bandwidth.

Incidentally, I don't think any SCSIe drives exist. I'm not sure if that's because NVMe is the superior protocol, or if it's just because NVMe was first to market.

I never heard of scsi express either.
not sure of differences either between scsi and nvme controller. the nvme spec says tons of protocol specific features. I did not make effort to do a side-by-side comparison