Samsung SM951 AHCI write speed reduced

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
Hi, I'm having something strange with my AHCI SSD. This is a Samsung SM951 model installed on a PCIe Lycom DT-120 card (PCIe port # 4), it is 256GB, has 124GB of free and TRIM is enabled.
It's been installed for a year and a half, at the time, I had Sierra and I remember more exactly but when I did tests of speed with Blackmagic Dsik Speed Test, I had about 1400-1500 mb / s in writing and reading.

Since then I moved to Mojave, I have 10.14.1 right now and 140.0.0.0.0.

There is little to be a month (I was already on Mojave) I did a speed test and I ended up with 1200mb / s in writing and 1400m / s in reading, I do not worry more that.

Today, I test again and I have 800 MB / s write and 1380 MB / s read.

Would you have a track to know what I just did, why this write speed loss?

Thank you for your opinions;)
 

tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
Hi, I'm having something strange with my AHCI SSD. This is a Samsung SM951 model installed on a PCIe Lycom DT-120 card (PCIe port # 4), it is 256GB, has 124GB of free and TRIM is enabled.
It's been installed for a year and a half, at the time, I had Sierra and I remember more exactly but when I did tests of speed with Blackmagic Dsik Speed Test, I had about 1400-1500 mb / s in writing and reading.

Since then I moved to Mojave, I have 10.14.1 right now and 140.0.0.0.0.

There is little to be a month (I was already on Mojave) I did a speed test and I ended up with 1200mb / s in writing and 1400m / s in reading, I do not worry more that.

Today, I test again and I have 800 MB / s write and 1380 MB / s read.

Would you have a track to know what I just did, why this write speed loss?

Thank you for your opinions;)
Boot single user mode and force trim, you have to do this from time to time, TRIM on SM951 needs some help.

Code:
fsck -fy
How to Repair a Mac Disk with fsck from Single User Mode
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
Hello @tsialex, sorry I use google translation and sometimes I have a little trouble with the translation :)

In the details of connected disks, it is well mentioned that this disk has the trim of activated.

Do I still have to force it again with the sudo trimforce enable command?
What do you mean by single user mode, I have only one user on my Mac and he is administrator, so it's ok?

Finally, the command fsck -fy will repair the disk? no problem for the data?

Sorry, I'd rather ask again to be sure of the translation, thanks
 

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tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
Hello @tsialex, sorry I use google translation and sometimes I have a little trouble with the translation :)

In the details of connected disks, it is well mentioned that this disk has the trim of activated.

Do I still have to force it again with the sudo trimforce enable command?
What do you mean by single user mode, I have only one user on my Mac and he is administrator, so it's ok?

Finally, the command fsck -fy will repair the disk? no problem for the data?

Sorry, I'd rather ask again to be sure of the translation, thanks
SM-951-AHCI TRIM support is buggier and needs more than just trimforce enable.

You need from time to time boot Single User mode and run fsck -fy to really TRIM the blade.

It's safe. Try it.

Another thing, if you are not using a heatsink maybe you are hitting thermal throttling. Install DriveDX and check the health of your blade.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
ok, so I do it again:

sudo trimforce enable
then
fsck -fy

No need to disable / enable SIP?

Finally, is it normal for the SSD's EFI file system to be in MS-DOS FAT32? I have already asked the question.

Thank you
 

tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
ok, so I do it again:

sudo trimforce enable
then
fsck -fy
No need to do trimforce enable again if TRIM is already enabled. Just boot Single User Mode and do the fsck -fy.

No need to disable / enable SIP?
No.

Finally, is it normal for the SSD's EFI file system to be in MS-DOS FAT32? I have already asked the question.

Thank you
Yes. EFI specification mandates the EFI folder to be FAT32.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
I have this error with de command fsck -fy

warning: option -f is not implemented, ignoring

error: container /dev/rdisk3 is mounted with write access.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
actually I did not know how to boot into a single user. unfortunately, command + s does not work at home, I have a black screen (I had to restart the mac by letting finger press power). That must come from the fact that I do not have bootscreen with my RX580. :(
 

tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
actually I did not know how to boot into a single user. unfortunately, command + s does not work at home, I have a black screen (I had to restart the mac by letting finger press power). That must come from the fact that I do not have bootscreen with my RX580. :(
You will need a install the original Apple GPU.

Since you will need to boot Single User Mode frequently to run fsck -fy to recoup performance, maybe it's better to think into changing the SM951-AHCI for another blade that have TRIM working correctly.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
How often do I have to restart in Single User Mode with the SM951-AHCI?
I have never tried, but can I use the gt120 while I am with Mojave?
Do you have an SSD drive to advise for more problems?
Thanks for your help
 

tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
How often do I have to restart in Single User Mode with the SM951-AHCI?
Every time the write speeds decrease, this depends on how much do you write.

I have never tried, but can I use the gt120 while I am with Mojave?
It shows the screen, but without acceleration.

Do you have an SSD drive to advise for more problems?
Thanks for your help
I replaced my SM951-AHCI 512GB with a 970 PRO 512GB.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
Thanks @tsialex pity I did not think there was this problem with this SSD. Tomorrow, I would use the command with my GT120 and I would control the flow often, for the moment I do not feel the loss of speed and that does not bother me.

But suddenly, I will look in more detail the eventual promotions on SSD nvme.
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
Hello, I'm placing the command fsck -fy, but I do not know if it went well. I see that there are "snapshot" errors (I use CCC without snapshot and Time Machine).

PS: I erased the 9 Snapshots, doing again the command fsck -fy it always puts the same error (there is only 1 Snapshots now). I passed SOS utility disk which also tells me the same error of Snapshots.
 

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Last edited:

zedex

macrumors regular
Oct 21, 2018
163
62
Perth, WA
Another forum member (@crjackson2134 I think) has noted that the SM951 write speeds fall away (become slower) when users convert from HFS+ to APFS (as you have done with your upgrade to Mojave).
 

tsialex

macrumors 604
Jun 13, 2016
7,856
8,481
Brazil
I can confirm that too :(
It's not the same thing.

APFS have a minor influence, at most 10% slower, with write speeds and happens with all drives.

SM951-AHCI write decrease speed is caused by the buggy TRIM algorithm and when the drive is full and with a lot of writes, sustained write speed can decrease to around 250MB/s or less.

When your blade is empty and trimmed, write speeds are normal. After some time, your drive will use all the empty cells and with the buggy TRIM, cells are being erased before written and this is the cause of the slow write speed.

With a drive that have a working TRIM, cells start to be erased after the OS marks it as deleted, this don't happen with SM951-AHCI. Any drive with correctly working TRIM will erase the cells in the background.
 
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marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
ok, I understand better :) An idea for this error with fsck -fy? I'm afraid of having to format everything. This error is identical in fsck -fy and disk utility

Capture d’écran 2019-03-12 à 14.19.10.png
 

marioliv66@

macrumors member
Original poster
Oct 2, 2017
58
4
France
for a APFS device the command is:

fsck_apfs -y -x
Could this command solve the problem of Snapshots error?
To pass I have to command + at startup, or I can do from the terminal? (I just removed from the GT120 to return the RX 580 :D)
 
Last edited:

nico5.1

macrumors newbie
May 17, 2017
4
0
Hello,

I think same problem here on a 2010 5.1 - 10.12.6 - dual 3,33 - 32gb ram - gtx980

I have 2 sm951 512 GB ahci on a Amfaltec squid blade since 2 years.. they are striped in raid 0 and it's my boot drive
At that time speed test (blackmagic) shows around 2500mb/s write and read speeds
I just ran the test 10 minutes ago : 220mb/s write and 1450mb/s read
Trim is enable since I bought them 2 years ago
I just tested the fsck command in single user and then rebooted... ran the speed test again... no real write speed improvement :-( but read speed is much better :)

Any ideas/solutions from the experts ? This is far beyond my knowledge

I love so much those machines ;) want to keep it as long as possible
 

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jd.fordyce

macrumors newbie
Dec 17, 2019
2
0
Boot single user mode and force trim, you have to do this from time to time, TRIM on SM951 needs some help.

Code:
fsck -fy
How to Repair a Mac Disk with fsck from Single User Mode

Hey guys I'm new to the forum but really need help and I think you're the right people to help me. I have a 2010 Mac Pro 5,1 with a 512GB Samsung SM951 which is experiencing reduced performance. From what I'm reading here it looks like I need to boot into single user mode and force trim.

however my problem is that when I try to boot into single user mode (cmd + s) nothing happens. i hear the boot chime but then it just does nothing. I've held cmd+s for up to 10 minutes hoping that maybe it just takes time, but it never does anything and I eventually just have to reboot it. I've experienced the same problem when I was trying to clean install High Sierra and was trying to cmd+opt+R. Nothing happened. I think it would let me boot into cmd+r though, but not the others. Any solutions to this problem? Thank you!
 
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