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zalle

macrumors regular
Original poster
Jun 2, 2008
224
9
Hi guys, I own a 2015 27" iMac, and I'm using an external SSD drive through usb 3.

It's got thunderbolt 2, which is supposed to be 4x faster than usb3.

Can I use an external thunderbolt ssd with the system and boot it from there? Ideally I want a 2TB SSD.

I don't seem to find such devices for sale, only thunderbolt 3, which has a different connection.

Thanks for your help.
 

Juicy Box

macrumors 604
Sep 23, 2014
7,540
8,876
Can I use an external thunderbolt ssd with the system and boot it from there?
Yes. Even if speeds were identical, there are actually benefits of using TB over USB as your boot drive.

TB SSDs have TRIM support on MacOS, something that USB SSDs do not. Having TRIM will extend the life of the SSD and keep it running at full performance for longer.

Most people do not have issues with USB SSDs, but you do occasionally see a TRIM, or a lack of TRIM, related issue on the forum.

The biggest reason people use USB over TB for SSDs is that USB is much cheaper for a decent enough speed.


I don't seem to find such devices for sale, only thunderbolt 3, which has a different connection.
There are hardly any TB1 and TB2 SSDs out there, and the ones that are out there are very pricey.

I have purchased a few TB1 HDDs over the years, and pulled the HDD out, put in a SATA SSD. This probably won't get you the faster speed you are looking for though.

It requires a TB3 Dock or a TB3 Drive that has its own power source, but you can use TB3 SSDs, such as a NVMe SSD, on TB1 and TB2 Macs. It require the expensive bidirectional adapter that Apple sells. You can sometimes find them for half the new price for a used one on eBay. You need a TB3 Dock or a drive that has its own power source because the power to run TB3 devices will not be available via the TB1/2 port.

It is expensive and requires the extra equipment (dock, bidirectional adapter), so not worth it to most when a USB SSD is usually a decent improvement on older/failed internal drives, which is why most people use the external boot drives.

I don't have TB2 Mac so I can't test it, but on my TB1 Macs, I am able to get over 900MBps sequential speeds using a TB3 NVMe SSD in the Samsung X5 drive.

It's got thunderbolt 2, which is supposed to be 4x faster than usb3.
It totally depends on the SSD Drive you are using. A NVMe over TB2 would probably will be faster, although, maybe not 4x. Probably 2.5-3 times faster.
 

zalle

macrumors regular
Original poster
Jun 2, 2008
224
9
Hi, thanks for your detailed answer.

I was thinking about a nvme SSD + a casing.

Do you know what casing would be suitable? Where/how to find it? I'm in Europe.

I'm getting just over 400MBps read/write over usb.
 

ovbacon

Suspended
Feb 13, 2010
1,596
11,505
Tahoe, CA
Hi guys, I own a 2015 27" iMac, and I'm using an external SSD drive through usb 3.

It's got thunderbolt 2, which is supposed to be 4x faster than usb3.

Can I use an external thunderbolt ssd with the system and boot it from there? Ideally I want a 2TB SSD.

I don't seem to find such devices for sale, only thunderbolt 3, which has a different connection.

Thanks for your help.
I have a 2015 5K iMac and it is running off a external 2TB ssd through usb3. As you I tried to go the tb2 route but couldn't find any normal priced cable to go from tb2 > tb3 (external ssd). Anything tb2 seems to be extremely pricy and the few I've seen that used it were unimpressed by results.

I just made sure the cable I had for my ssd enclosure was very good and I get 400mbps r/w which is good enough for this machine. I just don't restart it very often since that seems to take a really long time... everything else once running seems pretty good.

I do not use it as my main as I have a new mini M2.
 

zalle

macrumors regular
Original poster
Jun 2, 2008
224
9
The Lacie rugged thunderbolt drives wouldn't de any faster. Would they?. The bottleneck would be the SATA 500MBps, wouldn't it?
 

ovbacon

Suspended
Feb 13, 2010
1,596
11,505
Tahoe, CA
The Lacie rugged thunderbolt drives wouldn't de any faster. Would they?. The bottleneck would be the SATA 500MBps, wouldn't it?
nope they wouldn't be... If you really want to make that iMac fast again you kinda need to replace the internal hdd (fusion drive) with an ssd. That seems to really work for people but it comes at some risk. My iMac has screen damage and so it wasn't worth replacing the internal fusion with an ssd and have a brand new screen put on.

And like I said I have no experience with connecting an external ssd through tb2 but the arguments that I have seen here on MR seem to not indicate a massive speed increase.
 

Juicy Box

macrumors 604
Sep 23, 2014
7,540
8,876
I was thinking about a nvme SSD + a casing.

Do you know what casing would be suitable?
I don't know of any new NVMe enclosures for TB1/2.

Transcend makes a TB2 enclosure that is a package deal with their NVMe (JetDrive 855), so maybe that could be used with other brands' NVMe SSDs, but I don't know for sure.

Even if it does, Transcend doesn't advertise the speeds of their enclosures, just the NVMe that comes in the enclosure. Plus they are really expensive, you might as well just go the TB3 NVMe option or just stick with the USB3.


just don't restart it very often since that seems to take a really long time... everything else once running seems pretty good.
I know about weird boot issues.

I have a lot of iMacs, two are 27" Late 2012 and two are 27" Late 2013 iMacs. Of those four, three have/had Fusion Drives, and one with a HDD.

All had the HDD fail at least once, one more than once.

I noticed that they all had slower than normal boot times when running on an external drive. It didn't matter if the external drive was USB or TB. They would run fine after the boot was done.

The iMac with only the HDD actually had the worse boot times when booting externally, it would seem to hang at the very beginning, only to slow boot, then run great after booting.

When I installed Catalina on the HDD iMac (again, on an external, the internal HDD totally failed), the boot times got really bad, but would run great once booted for about 15 minutes then I would a kernel panic and auto restart.

This didn't happen on the same model, just with a failed Fusion Drive instead of a failed HDD.

Used the same external to boot into the Mojave partition, and it was less slow and no Kernel Panic.

BTW, replacing the internal HDD with a SATA SSD corrected all the goofy behavior.


But, I think the boot issues are being caused by the boot loader trying to find drives that are not working.



The Lacie rugged thunderbolt drives wouldn't de any faster. Would they?. The bottleneck would be the SATA 500MBps, wouldn't it?
I am not sure how it would be on TB2, but I have a LaCie Rugged TB1 enclosure that original had a HDD in it, and I swapped it for a SATA SSD.

On TB1, it is on par with USB3. The upside is that it has TRIM.

Another upside is that it works great on older Macs with only USB2, but has TB1, such as the Mid 2011 iMac, which I have two of them.
 

Fishrrman

macrumors Penryn
Feb 20, 2009
28,729
12,843
Where are you going to FIND a thunderbolt2 drive now?

"I was thinking about a nvme SSD + a casing"

I doubt you're going to find one of these (at least in tbolt2) anywhere.

My advice:
Keep using the USB3 setup you have now.
Put any money you would have spent towards a new Mac -- the 2015 is now 8 years old, going on 9.
 
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SaSaSushi

macrumors 601
Aug 8, 2007
4,156
553
Takamatsu, Japan
I've been using a Delock 42510 Thunderbolt 2 enclosure for almost 10 years now and it's still going strong.

I originally used it to boot my Late 2013 iMac. I loved it so much I bought Apple's overpriced TB3 to TB2 adapter cable to keep using it with my 2017 iMac and am still using it to this day for daily CCC clone backups.

It is still out there. You can get one here:


If you don't mind a beaten up box you could save $15 on eBay.

 
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