PCI-E vs. SATA Storage

no1statistician

Commendable
Aug 21, 2016
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I'm aware PCI-E is faster and more expensive as storage compared to SATA SSD. I'm also planning to use 8 lanes for my PCI-E. What is the noticeable different in computer boot times, installation, and reading and writing files to storage?
 
Solution
Snip-paste:

For most people, the NVMe SSDs simply aren't worth it. The reason is that MB/s is the inverse of how we perceive drive speed. We don't think a drive is fast because it has high MB/s, we think it's fast because we don't have to wait as long for it to finish a tasks - sec/MB.

If you compare these drives in sec/MB, you'll find that the bigger MB/s becomes, the less difference it makes. Say you're copying 1 GB of sequential files.

125 MB/s HDD = 8 sec
250 MB/s SATA 2 SSD = 4 sec
500 MB/s SATA 3 SSD = 2 sec
1000 MB/s NVM SSD = 1 sec
2000 MB/s NVM SSD = 0.5 sec

Notice how every time MB/s doubles, the additional time saved is halved? So even though the jump from an early 1000 MB/s NVM SSD to a newer 2000 MB/s NVM SSD sounds...

Rogue Leader

It's a trap!
Moderator


Honestly you would never even notice the speed difference in boot times. Where you do notice it is in heavy I/O operations, IE copying files on the drive, loading files from the drive. Installations are still limited by what you're installing from.

How are you "planning to use 8 lanes for your PCIe". The best NVMe drives only use 4 lanes. What is your concern here, running over lanes your GPU may use? What hardware are you using?
 

USAFRet

Titan
Moderator


Reading and writing files to 'storage' is also dependent on the target device.
No matter how fast your uber PCIe drive is...an HDD can only accept data so fast.
The PCIe drive is just idling along.

As with anything, performance depends on the speed of the slowest device in the chain.
 

no1statistician

Commendable
Aug 21, 2016
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I have a rx 480 gpu and a z170-a motherboard. I guess the only heavy IO tasks would be intermediate machine learning, but I'm not sure if writing to storage would be the bottleneck or gpu multi threading.



 
Snip-paste:

For most people, the NVMe SSDs simply aren't worth it. The reason is that MB/s is the inverse of how we perceive drive speed. We don't think a drive is fast because it has high MB/s, we think it's fast because we don't have to wait as long for it to finish a tasks - sec/MB.

If you compare these drives in sec/MB, you'll find that the bigger MB/s becomes, the less difference it makes. Say you're copying 1 GB of sequential files.

125 MB/s HDD = 8 sec
250 MB/s SATA 2 SSD = 4 sec
500 MB/s SATA 3 SSD = 2 sec
1000 MB/s NVM SSD = 1 sec
2000 MB/s NVM SSD = 0.5 sec

Notice how every time MB/s doubles, the additional time saved is halved? So even though the jump from an early 1000 MB/s NVM SSD to a newer 2000 MB/s NVM SSD sounds like a big deal (+1000 MB/s), it only shaves 0.5 seconds off this hypothetical copy. Whereas what looks like a small jump (SATA 2 SSD to SATA 3 SSD, +250 MB/s) saves 4x as much time - 2 seconds.

Or put another way, compared to the speedup you get from upgrading a HDD to a 2000 MB/s NVM SSD (7.5 seconds):

A 250 MB/s SATA 2 SSD gives you 53% of the speedup
A 500 MB/s SATA 3 SSD gives you 80% of the speedup
A 1000 MB/s NVM SSD gives you 93% of the speedup
A 2000 MB/s NVM SSD gives you 100% of the speedup

The bulk of the speedup is at the lower MB/s speeds. Since the SATA 3 SSD gives you 80% of the speedup (wait time reduction) of a 2000 MB/s NVM SSD, most people aren't going to notice the difference between the two in normal everyday use.

On top of that, sequential speeds are the fastest so have the least impact on overall wait times. It's the slowest speeds of the drive which force you to wait longer, so they have the biggest impact on wait times. If you're reading 1 GB of sequential data and 1 GB of small file data:

NVMe SSD (2 GB/s seq, 50 MB/s 4k) = 0.5 sec (seq) + 20 sec (4k) = 20.5 sec total
SATA 3 SSD (500 MB/s seq, 50 MB/s 4k) = 2 sec (seq) + 20 sec (4k) = 22 sec total
Difference of just 7%.

So people really should be comparing SSDs based on their 4k speeds, since that's the slowest. And pretty much every NVMe SSD I've seen still has non-queued 4k speeds far below the SATA 3 bandwidth limit.

The only real-world tasks significantly impacted by sequential speeds are real-time video editing, and copying large amounts of sequential data (e.g. movies or backup files) from one SSD to another equally-fast SSD.
 
Solution

Rogue Leader

It's a trap!
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A Z170 Board has 20 PCIe lanes in addition to the 16 lanes the CPU provides to your GPU. The PCIe M.2 slot is wired to those 20 lanes the PCH of the Z170 has so you have nothing to worry about in terms of running out of lanes if thats your concern.