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External SSD trim?

Calby

Calby

macrumors 6502
Original poster
Dec 30, 2015
332
40
Sweden, Gävle
Hi,
How can I make the performance from my external SSD as good as possible?
Is trim enabled on it?

I did read somewhere that you should make free space of 30GB ( don't even make it a partion just leave 30GB) to maximum the performence is that correct?

I'm running the mbp 2015 with sierra and the SSD is a Samsung T3 500GB with USB 3.1.
 
I think you'll have to force TRIM on. It isn't necessarily supported by the USB bridge chip in the SSD however. Not all bridge chips support TRIM.

In terms of leaving space free, SSDs do perform better with some free space, but there's already a portion of the SSD that is "over provisioned" as it's called. This is how it is straight from the factory. It may be a conservative amount, and leaving a bit more free could potentially be beneficial still, but honestly, I'd say don't worry about it.
 
casperes1996 said:
I think you'll have to force TRIM on. It isn't necessarily supported by the USB bridge chip in the SSD however. Not all bridge chips support TRIM.

In terms of leaving space free, SSDs do perform better with some free space, but there's already a portion of the SSD that is "over provisioned" as it's called. This is how it is straight from the factory. It may be a conservative amount, and leaving a bit more free could potentially be beneficial still, but honestly, I'd say don't worry about it.
Click to expand...

Ok so should I force trim on it or just leave it as it is?
 
Calby said:
Ok, but how do I know if it works or not?
If trim works, do I still need to leave a "unpartion"?
Click to expand...
It is not going to work. macOS does not support TRIM over USB.

Either way, there is no need to worry about leaving free space. As @casperes1996 mentioned, the disk is already "over provisioned" to allow for this. You might notice a little speed drop if the drive gets close to full, but otherwise, don't sweat it.
 
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Calby said:
Ok, but how do I know if it works or not?
If trim works, do I still need to leave a "unpartion"?
Click to expand...

I think you should be able to see if it's TRIM enabled through System Information, though not sure if it shows with USB connected disks.
The free space and TRIM thing are things that are meant to compliment each other actually, but as mentioned before, and as @Weaselboy refers to, it's not something you ought to actively think about. Just use the drive, and the controller inside it will manage the rest.
 
casperes1996 said:
I think you should be able to see if it's TRIM enabled through System Information, though not sure if it shows with USB connected disks.
Click to expand...

It is not going to show because TRIM won't work over USB with macOS. There are some enclosures that support UASP and Windows can TRIM (sort of). Here is a copy pasta of an earlier post.

Weaselboy said:
You are correct. USB cannot pass along the SATA TRIM command.

What some people have read and it has caused confusion, is some UASP (USB-attached SCSI protocol) enclosure chipsets can convert the SCSI Unmap command (similar to TRIM) to TRIM commands at the drive. Windows can run this SCSI Unmap command with the Powershell command Optimize-Volume and the -ReTrim option. OS X cannot run the SCSI Unmap command (at least not that I have been able to find). So at this point, no matter what chipset you use, you are not going to get TRIM over USB on a Mac.

There is some discussion at the bottom of this article.
Click to expand...
 
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TRIM nowadays is overrated. I have been running SSDs on my 2010 Mac Pro for years without TRIM enabled. Maybe on the cheapo drives it is an issue. But I have not encountered any issues on Crucial or Samsung SSDs running without TRIM for years.
 
Ok, sounds good will install it tomorrow and hoping to have a good speed.
Did read something about sat drive installation but I guess that if I need it macOS will install it to me or prompt me about it.

How can I test the speed? According to Samsung it should bee 450mb/s / 450mb/s
 
Weaselboy said:
It is not going to show because TRIM won't work over USB with macOS. There are some enclosures that support UASP and Windows can TRIM (sort of). Here is a copy pasta of an earlier post.
Click to expand...

Thanks for the information. I wasn't sure about this myself – D'you think we'll see better UASP support on macOS in future? I'm in the market for an enclosure in the near future, and had been looking for something that supports UASP, but if it bears no benefit on macOS and won't there's no point in limiting my search.

xWhiplash said:
TRIM nowadays is overrated. I have been running SSDs on my 2010 Mac Pro for years without TRIM enabled. Maybe on the cheapo drives it is an issue. But I have not encountered any issues on Crucial or Samsung SSDs running without TRIM for years.
Click to expand...

I think you've misunderstood the point of TRIM. It's not that running without will cause issues or anything. It's just for optimising the speed of SSDs as they fill up. If you imagine you have a room. Throwing a box into the room can be done relatively fast, but once the room fills up, you have to start removing boxes, before you can throw in a new one. This takes slightly longer. But what if, when you remove a box from the room and don't replace it, you would still have to go in the room when you want to put another box in there, and go to the place where there previously was a box, and "remove" the already removed box to put a new one in there? You'd be wasting time. That's what TRIM avoids.
If you wipe your SSDs entirely right now, and start using them, until they're full, they'll run at a specific speed. When they then get full, you'll see a slowdown - now, it isn't a fixed slowdown and depends on the drive, but let's just say 20%. Even if you remove data from the drive, this slowdown might still be there, due to TRIM not being active, sending commands to the drive about which blocks are safe to erase entirely, after the file link has been removed.

Calby said:
Did read something about sat drive installation but I guess that if I need it macOS will install it to me or prompt me about it.
Click to expand...

I have no idea what you're talking about, but the drive should function perfectly fine with no software installed.

Calby said:
How can I test the speed? According to Samsung it should bee 450mb/s / 450mb/s
Click to expand...

There are loads of drive testing apps. I personally use BlackMagic as another user suggested, and it's a quick download from the App Store. I can also recommend ATTO, and you can also manually calculate it, by timing a file transfer
 
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casperes1996 said:
Thanks for the information. I wasn't sure about this myself – D'you think we'll see better UASP support on macOS in future? I'm in the market for an enclosure in the near future, and had been looking for something that supports UASP, but if it bears no benefit on macOS and won't there's no point in limiting my search.
Click to expand...

I have not read anything about that SCSI UNMAP command coming to macOS. I have read about the new APFS Mac file system coming, but nothing I have seen related to that mentions this SCSI command.

I would still get a UASP enclosure though because they are usually faster.
 
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Weaselboy said:
I have not read anything about that SCSI UNMAP command coming to macOS. I have read about the new APFS Mac file system coming, but nothing I have seen related to that mentions this SCSI command.

I would still get a UASP enclosure though because they are usually faster.
Click to expand...

Thanks!
Also, I don't think that anything about the file system relates to UASP. I've already done some tests with APFS however, and it's a lovely file system. Can't wait to replace all HFS+ with it. Already rocking it fully on my iOS devices, and have used it for smaller images on on macOS, but that's not really fair since that's an APFS image inside HFS+
 
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Weaselboy wrote:
"It is not going to work. macOS does not support TRIM over USB."

This is correct for USB3 Gen1, up through the 2015 product line of Macs, but...
...I've read reports (over at Macintouch.com, I believe) that with USB-c and USB3.1 Gen2, TRIM -has been- indicated as being active on a few external drives. At least while using Disk Utility's repair disk function, DU reports "unused blocks" are being TRIM'ed.

Just a few reports so far, and perhaps those doing the reporting were misled by "what they saw".

I'm wondering if the USB 3.1 Gen2 specs (perhaps incorporating improvements in UASP) now include the ability to send TRIM commands via USB?

Can't say for certain, yet. More reports are needed.

But I've posted this before, and will state my opinion again:
For the overwhelming majority of USB3 drives connected to a Mac, the "lack of TRIM" will make NO DISCERNIBLE DIFFERENCE over the lifetime of the drive, so long as the user leaves a sufficient amount of "free space" available. I've used an "external booter" SSD connected vai USB3 for more than four years now, and it runs as well as when it was first connected. TRIM has never become an issue. YMMV.
 
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Fishrrman said:
For the overwhelming majority of USB3 drives connected to a Mac, the "lack of TRIM" will make NO DISCERNIBLE DIFFERENCE over the lifetime of the drive, so long as the user leaves a sufficient amount of "free space" available. I've used an "external booter" SSD connected vai USB3 for more than four years now, and it runs as well as when it was first connected. TRIM has never become an issue. YMMV.
Click to expand...

A good drive without TRIM is better than a bad one with TRIM, but it's still nice to have. Wish I had hardware to test with, whether it's actually there on the USB 3.1 Gen 2 Macs.
 
casperes1996 said:
Can I ask about testing methodology? Not that I don't think you're competent in terms of testing it, but just in case there may be potential workaround options.
Click to expand...
I'm just looking at the drive and enclosure in system report and it does not show TRIM.

On a drive with TRIM Disk Util will show that unused blocks message @Fishrrman mentioned and I'm not seeing that either.
 
To all:
See this post from macintouch.com:
https://www.macintouch.com/forums/showthread.php?tid=799&pid=15537#pid15537
===
I have much the same system as Ric describes, except I used the StarTech.com USB 3.1 Gen 2 (10 Gb/s) mSATA Drive Enclosure (SM21BMU31C3) in place of the Sabrent. I use this system as my boot and data drive at work and at home; I carry it back and forth in my shirt pocket.

StarTech claims to support Trim on this USB-SATA enclosure: "If the OS issues a TRIM command, the command will be passed to the connected device."

When I run Disk Utility (First Aid) on this device, it does include the line "Trimming unused blocks." after the normal checks. Anyone know more about this specific operation on a USB -> SATA connected SSD? Is this verification that the TRIM command has been run by the SSD's internal controller?

My Blackmagic Disk Speed Test (5 GB) results from a USB 3.1 Gen 1 (5 Gb/s) port and using the 1TB Samsung 850 EVO M.2 SSD are:

423.3 MB/s Read and 430.1 MB/s Write.
===
Here is the product the macintouch poster above is commenting about:
https://www.amazon.com/StarTech-com...intouchforums-20?&tag=macintouchforums-20
 
Last edited:
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Fishrrman said:
When I run Disk Utility (First Aid) on this device, it does include the line "Trimming unused blocks." after the normal checks. Anyone know more about this specific operation on a USB -> SATA connected SSD? Is this verification that the TRIM command has been run by the SSD's internal controller?
Click to expand...


Honestly, I'm a bit confused at this point. It is definitely not confirmation that the controller received the TRIM commands and handled them, but to me, it does seem like confirmation that macOS tried issuing said command, and most likely they were processed correctly. But I wouldn't say it's certain. Though since Disk Utility didn't report an error message, I assume that's the green light in terms of it working?
 
That same person posts this later in the thread, so I remain unconvinced. USB does not support the TRIM ATA command. Windows is doing this by issuing the SCSI UNMAP command to achieve the same effect, but it is not really using the TRIM command either.

The external USB-mounted SSD is listed under Storage and under USB within the System Information report. However, in neither place can I find any line that mentions the Trim property whatsoever.

Of course there is a "TRIM Support" line in the SATA category report on the internal, Apple SSD. However, the external USB-mounted SSD device is not listed in this category at all, even though it is a SATA device using USB Attached SCSI Protocol (UASP), which I just verified via "ioreg".
Click to expand...
 
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