Slow SSD after iMAC upgrade

[kazaka]

Hi guys,

I just have upgraded my iMac 27" mid 2015 with a 1TB NVMe Samsung EVO Plus and I am getting low speeds results for this kind of SSD. before I was getting almost the same speeds as an external USB SSD drive.

Anyone knows why I am getting these low speed values ?? These are not normal speeds for these kind of Samsung SSD.

The way I did the upgrade:

I followed the ifixit video tutorial.

Before the upgrade I was using the SSD as an external SSD in the iMac with Mojave installed and it was working normal with speeds up to 500MB/s.

I decided to move the SSD and insert it on the logicboard of the iMac. I have bought for that this SSD NVMe adapter on eBay.

When the iMac was upgraded and closed the iMac powered well and in fact I am writing these line on it.

I do not understand why I get speeds about 600MB/s with this powerful Samsung SSD.

Should I need to re-format the SSD and install MACOSx again?

Adapter not good? Should I need to buy a Sintech adapter?



Here is some info from my system:

 

[tyc0746]

If memory serves, the Mid 2015 model was just a pared-down 2014 model at a cheaper price point before the Late 2015 models came out.

That would mean it has the slower 2x channel PCIe 2.0 interface of the 2014 models too, rather than the 4x channel PCIe interface of the Late 2015 onwards models.

BTW, the translation of the info in your screenshot actually tells you that you have 2 channels of 5GT/s (about 500mb/s) which confirms my suspicions.

Unfortunately that means you’ll be heavily under-utilising the 970 Pluses capabilities as the interface will max out at about 1000mbps (minus whatever overheads the bus/system uses).

You‘d probably get faster performance in a decent TB2 if you can find one (over 2000mbps) or USB 3.1 gen 2 (over 1000mbps) external enclosure.

 

[kazaka]

Hi,

So my Imac does not support fully the Samsung Evo plus capabilities... I have a TB2 dock and when I had that same SSD running externally throught the TB2 dock I was getting the same 600MB/s ... theres no difference at all... I think the SSD internaly is a bit faster than conected externaly through TB2 and USB 3.0.

 

[kazaka]

Maybe this is a silly question but do you think I can swap my iMac mid 2015 logic board with a compatible PCIe X4 logic board from another iMac model? I was thinking the late 2015 logic board (it has X4 PCIe).. do you think this logic board is compatible with the mid 2015 iMac case and connectors?

 

[tyc0746]

Was the SSD the only thing connected to the Thunderbolt dock? Was it connected via a Thunderbolt 2 cable or USB? Does the enclosure have a TB2 port?

If you've got a TB2 enclosure, then try connecting the drive directly to the TB2 port of the iMac and try a speed test again.

 

[kazaka]

The external EVO PLUS SSD was connected to the dock via USB 3.0 and the then dock to the iMac via TB2 connection.

The SSD Enclosure has a USB 3.0 cable to connect.

When I connected this SSD to the dock and then to the iMac nothing else then the external SSD was connected to the dock.

The EVO Plus SSD is inside of the iMac currently.

 

[tyc0746]

That's why the Thunderbolt hub didn't show any speed increase - the slowest part was still the USB3 connection - just connecting it to a faster port/hub won't magically speed up the connection as ALL parts of the route need to support that speed.

The only port on your machine that will support a higher speed is the TB2 port - and ONLY if you connect it to a TB2 enclosure (or TB3 enclosure [like this OWC Envy Express] with an TB3-TB2 adapter [such as this Apple one]) and a TB2 cable.

I can't help any further on specifics as I have an older TB2 Thunderbay 4 with 4 slower/cheaper SATA SSDs in, and most of my external SSDs are USB3.1 only (which give a max of about 1000mbps for a Sandisk Extreme) which I use to share between machines at different locations.

 

[kazaka]

What would be the speeds of the OWC TB3 enclosure running through TB2 connection?

 

[tyc0746]

What would be the speeds of the OWC TB3 enclosure running through TB2 connection?

The same as running it via a TB2 enclosure/cable/port - i.e. slowest part of the route - so 2000-2400mbps (connection has max of 20GBps).
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[kazaka]

But what are the differences between the TB3 enclosure and the Raid system you use? Why you use a Raid System? The speeds are faster?

 

[tyc0746]

Not faster, just redundant back-ups - so that if one drive dies I've still got instant access to the data, as it's mirrored to another drive, and I simply pop in another drive to keep the system backed-up.

TB3 and TB2 are just a different generation of Thunderbolt. When I bought my enclosure there were not a lot of really fast/big/cheap SSDs around, so I had to stick to HDDs (4TB ones in my case). TB3 was not around in 2015, so the fastest I could buy was TB2 - which is what I did.

As my 2014 iMac will not make any benefit out of going to TB3, there seems to be little point in me spending another £500 for a TB3 storage bay - especially as the HDDs in there are only capable of about 130mbps.

 

[kazaka]

what do you recomend. me in this case?? a Raid box or a external SSD TB3 or keep the NVMe SSD inside of the iMac?

 

[tyc0746]

If you don't need the full speed the SSD can provide, then leave it where it is.

If you really do need the full speed then a Thunderbolt single blade enclosure would be the best option (e.g. OWX Envoy Express + Apple TB3 to TB2 adapter).

If you need lots of fast storage, then a TB3 RAID storage box is the best option (e.g. OWC Express 4M2), as you can expand it as you need - but it will still be limited to the total bandwidth of your TB2 port (20gbps).

I'd normally also suggest a USB3.1 Gen 2 (10gpbs) enclosure (e.g. relatively cheap IcyBox one or a prettier OWC Envoy Pro EX) - but your iMac's older USB ports are only USB3.0 (5gbps) so will still max out at about 600mbps.

 

[kazaka]

Today I just saw that the speed of the EVO PLUS SSD in a x4 iMac is 3000mb/s... its hard to believe that I get only 700mb/s with x2... Its a big drop in speed!!! Cant understand this big drop...

I cant have the SSD internally, at least this one because if I am in the iMac for some hours doing stuff the temperature reach about 93 degrees above the maximum allowed (85 degrees),..

Before I was with the Plugable external enclosure with the same SSD and connected via USB 3.0 and was having speeds of 500mb/s.

I open the iMac to put the SSD blade thinking I was going to have more speed but no.. the speed just increased a bit...

 

[tyc0746]

As I've said many times - the only way you'll get more speed is via Thunderbolt. I'm not sure what else I can tell you.

You WILL NOT get 3000MBps out of a mid-2015 iMac:

The late-2014 and mid-2015 iMacs have

• internal PCIe 2.0 x 2 (2 x 5GT/s or ~1GBps/1000MBps)
• 2 x external Thunderbolt 2 ports (20Gbps/2.5GBps/2400MBps)
• 4 x external USB-A 3.0 ports (5Gbps or ~500mbps)

The late-2015 iMacs have:

• internal PCIe 2.0 x4 (4 x 5GT/s or ~2GBps/2000MBps)
• 4 x externalThunderbolt 2 ports (20Gbps/2.5GBps/2400MBps)
• 4 x external USB-A 3.0 ports (5Gbps or ~500mbps)

The post-2017 iMacs have

• internal PCIe 3.0 x4 (4 x 8GT/s or ~3GBps/3000MBps)
• 2 x external Thunderbolt 3 ports (40Gbps/5GBps/5000MBps)
• 2 x external USB-C 3.1 gen 2 ports using the same port at TB3 (10Gbps or ~1200MBps)
• 4 x external USB-A 3.0 ports (5Gbps or ~500mbps)

The Samsung 970 Evo Plus also has a buffer/cache (intelligent turbowrite) where the transfer speed will be greater than the PCIe 3.0x4 speed until the cache is full, then it will slow down - but how/when you'd hit that limit, I don't know.

Sequential and random write performance was measured with Intelligent TurboWrite technology being activated. The sequential write performances for the portion of data exceeding Intelligent TurboWrite buffer size are: 400 MB/s for 250GB, 900 MB/s for 500GB, 1700 MB/s for 1TB and 1750 MB/s for 2TB

Apologies if I've mixed up any of the labels on the throughputs

 

[kazaka]

If i replace the hole mid 2015 logic board and replace it with a late 2015 logic board i would have those speeds as late 2015 is PCIe x4 ?

I saw both logic boards have the same perfurations and the place of the componentes is exactly the same. The way i would do is replace the hole logic board with its componentes for a late 2015 plus its components in my imAc mid 2015 chassis. I wouldnt be mixing componentes from the mid 2015 in the late 2015 logic board. It would be a straigh swap. I suppose the power supply is identical dor the late 2015.

Do you think this could be a solution?

 

[tyc0746]

Sorry, that's too technical for me.

I try not to take my machines apart if I can help it, as I know I'll break something else whilst I'm in there.

 

[r6mile]

If i replace the hole mid 2015 logic board and replace it with a late 2015 logic board i would have those speeds as late 2015 is PCIe x4 ?

I saw both logic boards have the same perfurations and the place of the componentes is exactly the same. The way i would do is replace the hole logic board with its componentes for a late 2015 plus its components in my imAc mid 2015 chassis. I wouldnt be mixing componentes from the mid 2015 in the late 2015 logic board. It would be a straigh swap. I suppose the power supply is identical dor the late 2015.

Do you think this could be a solution?

View attachment 928755

Sorry but why don't you just do as one of the other posters suggested, and get a TB2 enclosure? Replacing the logic board, even if it would work, seems way more expensive and a sure way of risking breaking something inside your iMac.