Question about external storage

[R3k]

Hey, why would a 4 x SSD Thunderbolt 3 drive enclosure such as the OWC Thunderbay 4 Mini only have a max transfer speed of around 1500 MB/s?

All 4 SSD drives at maximum read would be approx 2000 MB/ps and the thunderbolt 3 throughput is capable of much more (20Gb/ps = 1200 MB/ps and 40Gb/ps = 5000 MB/ps).

This reduced performance seems to be with all manufacturers. What is the limiting factor do you think?

 

[DeltaMac]

Ultimately, the limiting factor would be the throughput of the storage devices.
There would be overhead added with each device, which would likely be why you can't simply add all the individual speeds. But, SSDs are still pretty fast, and a RAID setup is going to be really fast, just not the speeds that you might think by adding numbers together. There's always overhead, and other performance losses with combined storage tech.

 

[R3k]

Ultimately, the limiting factor would be the throughput of the storage devices.
There would be overhead added with each device, which would likely be why you can't simply add all the individual speeds. But, SSDs are still pretty fast, and a RAID setup is going to be really fast, just not the speeds that you might think by adding numbers together. There's always overhead, and other performance losses with combined storage tech.

Thanks. Ill actually plan to run the drives in JBOD mode (non raid).
But yeah, its definitely the devices themselves, but as this reduced throughput seems to be with every multi drive device from every manufacturer I can find, I wonder what the specifics cause is?
An odd 25% performance loss is a lot of overhead.

 

[F-Train]

Hi @R3k

You may find it useful to have a look at this thread, which I started a couple of weeks ago on the same kind of issue: Thunderbolt 4 & NVMe M.2 External Storage: Read/Write Speeds?

I think that the numbers vary more than your first post suggests, and I'm pretty sure at this point that some enclosures do perform better than others. So do NVMe M.2 SSDs.

The upshot of that thread is that I decided to order a larger internal drive for my Mac Studio (see signature) and to have a smaller role for external storage, especially DIY NVMe storage.

 

[R3k]

Hi @R3k

You may find it useful to have a look at this thread, which I started a couple of weeks ago on the same kind of issue: Thunderbolt 4 & NVMe M.2 External Storage: Read/Write Speeds?

I think that the numbers vary more than your first post suggests, and I'm pretty sure at this point that some enclosures do perform better than others. So do NVMe M.2 SSDs.

The upshot of that thread is that I decided to order a larger internal drive for my Mac Studio (see signature) and to have a smaller role for external storage, especially DIY NVMe storage.

Thankyou, good reading. The thread(s) are more inline with people having inconsistent results with different hardware. Im wondering more in line with manufacturer published "best case" throughput numbers being lower than both the SSD speed and Thunderbolt speed.
If one can't can't even reach the theoretical speed, yeah, another big can of worms.

 

[DeltaMac]

Found this article - https://macperformanceguide.com/blog/2019/20190128_1352-understanding-Thunderbolt3-bandwidth.html
The idea that I can get from that article illustrates that you can't always compare specifications to real-world performance.

 

[F-Train]

Thankyou, good reading. The thread(s) are more inline with people having inconsistent results with different hardware. Im wondering more in line with manufacturer published "best case" throughput numbers being lower than both the SSD speed and Thunderbolt speed.
If one can't can't even reach the theoretical speed, yeah, another big can of worms.

The cap is the Thunderbolt 3 throughput speed. I believe that real world maximum TB3 speed, if all goes well, is more like 2700MB/s. I'm pretty sure that some enclosures are lower because of the enclosure design. So are some SSDs. I believe that the Samsung 970 EVO Plus write speed is about 1200MB/s regardless of enclosure. As it happens, I'm going to be able to test that SSD tomorrow.*

*Sonnet Tech has a PDF on compatibility of SSDs with its enclosures. There's a footnote about the Samsung 970 EVO Plus's write speed. The footnote is in accordance with a number of posts that I've read.

 

[R3k]

Found this article - https://macperformanceguide.com/blog/2019/20190128_1352-understanding-Thunderbolt3-bandwidth.html
The idea that I can get from that article illustrates that you can't always compare specifications to real-world performance.

Cool. Yeah, didn’t know that a large part of the bandwidth is only usable for video. Interesting. Shared busses~ important to know.

 

[F-Train]

Shared busses~ important to know.

I haven't read that article, but the Thunderbolt 4/3 busses on the Mac Studio are not shared.

 

[R3k]

Coo

I haven't read that article, but the Thunderbolt 4/3 busses on the Mac Studio are not shared.

Cool. Yeah, the article was using the 2019 iMac as an example.

 

[mcnallym]

Well the thunderbay 4 mini works with 2.5” SSD/HDD so going to be Sata devices.
If you look at the Express 4M2 which takes NVME drives then each drive only gets an x2 connection again limiting the speed can transfer off irrespective of the actual SSD installed where the SSD are usually designed with an x4 lane connection in mind,

 

[F-Train]

The cap is the Thunderbolt 3 throughput speed. I believe that real world maximum TB3 speed, if all goes well, is more like 2700MB/s. I'm pretty sure that some enclosures are lower because of the enclosure design. So are some SSDs. I believe that the Samsung 970 EVO Plus write speed is about 1200MB/s regardless of enclosure. As it happens, I'm going to be able to test that SSD tomorrow.*

*Sonnet Tech has a PDF on compatibility of SSDs with its enclosures. There's a footnote about the Samsung 970 EVO Plus's write speed. The footnote is in accordance with a number of posts that I've read.

See this post for the result of my Samsung 970 EVO Plus 2TB test: https://forums.macrumors.com/thread...orage-read-write-speeds.2340127/post-31032781

 

[R3k]

Well the thunderbay 4 mini works with 2.5” SSD/HDD so going to be Sata devices.
If you look at the Express 4M2 which takes NVME drives then each drive only gets an x2 connection again limiting the speed can transfer off irrespective of the actual SSD installed where the SSD are usually designed with an x4 lane connection in mind,

Yep.

The Express M2 NVM enclosure is able to fully saturate the Thunderbolt saturate the TB Buss (up to 2800 MB/ps)
The Thunderbay 4 Mini enclosure with 4 x SATA SSD's each being able to read at 550MB/ps can only use max 1556 MB/ps of the buss.

 

[F-Train]

Further to post #12, these are my results with a Samsung 2TB 980 Pro: https://forums.macrumors.com/thread...orage-read-write-speeds.2340127/post-31035631

In a Thunderbolt 3 enclosure, the write speed is double the speed of the 2TB 970 EVO Plus.

 

[F-Train]

At the request of @Ploki I've added results of a test of the Samsung 980 Pro using Amorphous Disk Mark: https://forums.macrumors.com/thread...orage-read-write-speeds.2340127/post-31036939

 

[R3k]

For some closure to this thread.

I had previously received incorrect information from Other World Computing. I contacted them again and have correct infos now.

The published speeds for OWC SATA SSD enclosures refer to Raid speed only. If the drives are configured as JBOD (Separate disks) then the enclosure does not come into play and the throughput is only limited by drive speed and thunderbolt bandwidth.

I should be able to get 2200 MB/ps speeds with all SSD’s at maximum read.

 

[atonaldenim]

For some closure to this thread.

I had previously received incorrect information from Other World Computing. I contacted them again and have correct infos now.

The published speeds for OWC enclosures refer to Raid speed only. If the drives are configured as JBOD (Separate disks) then the enclosure does not come into play and the throughput is only limited by drive speed and thunderbolt bandwidth.

I should be able to get 2200 MB/ps speeds with all SSD’s at maximum read.

Are you referring to the OWC Express 4M2 TB enclosure? Because I read a review that said each NVMe blade is only assigned x1 PCIe lane if used in JBOD mode. That it only achieves max quoted speed when all 4 blades are in a RAID0. Which kinda sucks, but makes sense given its relatively low price and no mention of a PCIe switch onboard.

 

[R3k]

Are you referring to the OWC Express 4M2 TB enclosure? Because I read a review that said each NVMe blade is only assigned x1 PCIe lane if used in JBOD mode. That it only achieves max quoted speed when all 4 blades are in a RAID0. Which kinda sucks, but makes sense given its relatively low price and no mention of a PCIe switch onboard.

This was regarding SATA SSD enclosures, such as the Thunderbay 4 Mini. I’ll edit my above post to be clearer.

On the lanes with blades, well it makes sense, unless the unit could somehow dynamically switch lanes on the fly to balance bandwidth; it seems a logical limitation. But yeah, interesting; it seems a completely different ballgame than with SATA.