External Bootable SSD Late 2015 iMac

plasticbag01

macrumors newbie
Original poster
Jan 22, 2019
2
1
New York
Hi All,

I'm looking to buy an external SSD and make it bootable for my late 2015 iMac. I'm open to any suggestions, but I'm thinking of this as a single dedicated drive (I don't need multidrive units). It's a 5k display, with USB 3 and Thunderbolt 2 ports. I'm looking for the fastest option available as it's going to a boot drive.

Thunderbolt 2 wasn't wildly popular and I'm having a hard time finding any drives, am I wasting my time? I don't mind putting drives into other enclosures, it doesn't have to be one stop shopping.

If anyone has had any success (or failures) with the above request please let me know. Any additional advice as well would be great.

Thanks in advance!
 
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ChrisA

macrumors G4
Jan 5, 2006
11,640
450
Redondo Beach, California
Buy a USB 3 SSD. Format it as APFS, install MacOS then use Apple's migration assistant to move you data and apps. Then change the default boot drive and reboot.

After using your new system long enough that you are sure there are now problems. and ADTER the first full Time Machine backup, then, erase the Mac Internal drive, make it also APFS and use it for storing bulk data that dose not need to be on the SSD.

The above is exactly what I did with my iMac. Also if you have no already done so install as much RAM as will fit the the iMac, just max it out.

YouTime machine backup drive does not need to be USB 3, it can be slow but you may as well use USB 3. Make sure this TM drive is at least 2X larger then al to data you have or will have

I would not erase (aka "reformat') the internal drive until after you are running a few data on the external SSD and Time Machine has finished it's first complete backup of the new SSD. Maybe even wait until our cloud backup is done? (If you don't have this, sign up for it. Backblaze is only $5 per month.)

One issue is keeping a usable backup while you make the switch. You have your old data i-on the old drive and I presume a Time Machine backup of this. To avoid accidents, unplug the tm drive and lock it in a drawer until after the transition is complete. This will prevent human error which is easier than you r think to do. Put the old TM drive is your desk at work, or see place far away. Buy a new TM drive for your new setup.
 

plasticbag01

macrumors newbie
Original poster
Jan 22, 2019
2
1
New York
Thanks so much for the replies, I'm surprised Thunderbolt is not recommended. I thought it was a faster option than USB 3, which would be important given it's a boot drive. Glad to hear USB 3 works.
 

Moonjumper

macrumors 68020
Jun 20, 2009
2,263
1,947
Lincoln, UK
Thanks so much for the replies, I'm surprised Thunderbolt is not recommended. I thought it was a faster option than USB 3, which would be important given it's a boot drive. Glad to hear USB 3 works.
While Thunderbolt is potentially better, price and availability gives USB3 significant advantages and only a small performance downside.
 

weckart

macrumors 603
Nov 7, 2004
5,004
2,241
I bought a cheap TB1 used drive and replaced the internal spinner for an SSD to use as the boot drive for my sister's 2015 iMac. The internal drive was a very slow 5400rpm. It wasn't that expensive to do. The main advantage is that TRIM is supported over TB but not over USB.
 

the-bigwig

macrumors member
May 17, 2016
65
155
Was in the same boat as you. Went with USB 3.0 enclosure with UASP support. What an improvement! About 370mbps/370mbps speeds versus 100mbps before. I suppose that's about 25% slower than Thunderbolt but well, you just can't notice it at all. The differences are imo not worth the cost of TB enclosure.
 

iMacGuru

macrumors member
Aug 18, 2009
33
3
Miami
I, too, am using an external SSD plus an external HDD for the Time Machine.All run great using USB 3. My internal fusion drive sits there awaiting some use. I'm running High Sierra because I was having continuous bouncing beach balls using Mojave.
 

SaSaSushi

macrumors 601
Aug 8, 2007
4,103
494
Takamatsu, Japan
Probably too late for the OP but $85 for the Delock 42510 Thunderbolt enclosure plus the price of a Thunderbolt cable was well worth it for me when invested in one about 5 years ago to boot my Late 2013 iMac (at the time).

I've since replaced that iMac with a 2017 iMac with 512GB SSD have been continuing to use the Delock to run BootCamp Windows. I had to invest in an Apple Thunderbolt 2 to Thunderbolt 3 cable but it was worth it. It's a great enclosure.

I definitely recommend Thunderbolt for an external boot SSD. Thunderbolt is faster and allows the use of TRIM. Even for that alone I recommend it.
 

multitudes

macrumors newbie
Feb 12, 2019
6
6
I agree with SaSaSushi on this one. The 2015 MBP has a very fast PCIe M.2 SSD which clocks at more than 1,400MBps for writes and more than 1,300MBps for reads. USB C has a max nominal bandwidth of 10Gbps which will be less than 1250 MB/s. This will be still fast but compared to the speed of the internal drive is a bottleneck. Now consider that Thunderbolt 3 has a 40 Mbps equal to max bandwidth of 5000 MB/s.
I read a nice article on Anandtech about this. They do not recommend the Samsung X5 due to thermal throttling issues but the TEKQ Rapide TB3 seems quite amazing.
 

ignatius345

macrumors 68030
Aug 20, 2015
2,679
3,594
Hi All,

I'm looking to buy an external SSD and make it bootable for my late 2015 iMac. I'm open to any suggestions, but I'm thinking of this as a single dedicated drive (I don't need multidrive units). It's a 5k display, with USB 3 and Thunderbolt 2 ports. I'm looking for the fastest option available as it's going to a boot drive.

Thunderbolt 2 wasn't wildly popular and I'm having a hard time finding any drives, am I wasting my time? I don't mind putting drives into other enclosures, it doesn't have to be one stop shopping.

If anyone has had any success (or failures) with the above request please let me know. Any additional advice as well would be great.

Thanks in advance!
Hey, how did this go? I've got very similar hardware to yours and have been considering the same upgrade. Thanks!
 

Bremse

macrumors newbie
Jan 30, 2020
3
1
Here is what I just did: 512 GB NVMe-based external Thunderbolt 3 SSD (was just $100 at Amazon). I connected it to a HP portable Thunderbolt 3 dock which is connected to an Apple TB3 to TB2 Adapter which is plugged into the iMac with an Apple TB2 cable. It’s a base model 27” late 2015 iMac with standard hard drive. I get read and write speeds of right around 1250 MB/sec. Booting works and no sleep issues either. It’s much faster than a USB3 drive and a ton faster than the internal spinner. I already had one but the HP docks are on eBay for cheap (get the travel version without attached TB3 cable - I’ve seen them as low as $50 with power adapter) and I got the TB adapter and cable off FB marketplace for a combined $25. Not the most elegant solution but it works very well and wasn’t too expensive. At some point I will upgrade the ssd in the enclosure with a larger one (it uses standard NVME blades). Note that NVMe is not supported in older MacOS versions but I’m running Catalina without issues. I would go with a thunderbolt drive of some sort due to the increased throughout. Another option I considered but would have been more expensive is a PCIe enclosure (either TB2 or TB3 plus the Apple adapter). You can install a PCIe to NVMe Adapter card and a standard NVMe blade drive. Speed should be about the same as it’s limited by TB2 to about 1200-1300 MB/s.
The HP dock also provides extra USB ports as well as Displayport but I haven’t tried a display yet (USB ports work).

Edit: You need a dock to power the TB3 drive since the drive is bus powered but the Apple TB2/3 adapter doesn’t provide power to the TB3 device. Also, the Apple adapter appears to be the only one you can use “backwards” to connect TB3 devices to TB1/2 Macs. Other adapters only allow connection of TB1/2 devices to TB3 Macs.
 
Last edited:

1ampaulPH

macrumors newbie
Jun 23, 2020
1
0
Here is what I just did: 512 GB NVMe-based external Thunderbolt 3 SSD (was just $100 at Amazon). I connected it to a HP portable Thunderbolt 3 dock which is connected to an Apple TB3 to TB2 Adapter which is plugged into the iMac with an Apple TB2 cable. It’s a base model 27” late 2015 iMac with standard hard drive. I get read and write speeds of right around 1250 MB/sec. Booting works and no sleep issues either. It’s much faster than a USB3 drive and a ton faster than the internal spinner. I already had one but the HP docks are on eBay for cheap (get the travel version without attached TB3 cable - I’ve seen them as low as $50 with power adapter) and I got the TB adapter and cable off FB marketplace for a combined $25. Not the most elegant solution but it works very well and wasn’t too expensive. At some point I will upgrade the ssd in the enclosure with a larger one (it uses standard NVME blades). Note that NVMe is not supported in older MacOS versions but I’m running Catalina without issues. I would go with a thunderbolt drive of some sort due to the increased throughout. Another option I considered but would have been more expensive is a PCIe enclosure (either TB2 or TB3 plus the Apple adapter). You can install a PCIe to NVMe Adapter card and a standard NVMe blade drive. Speed should be about the same as it’s limited by TB2 to about 1200-1300 MB/s.
The HP dock also provides extra USB ports as well as Displayport but I haven’t tried a display yet (USB ports work).

Edit: You need a dock to power the TB3 drive since the drive is bus powered but the Apple TB2/3 adapter doesn’t provide power to the TB3 device. Also, the Apple adapter appears to be the only one you can use “backwards” to connect TB3 devices to TB1/2 Macs. Other adapters only allow connection of TB1/2 devices to TB3 Macs.
Been looking for this! This is what I am planning to do. You mind posting the exact model of your HP dock and which NVMe enclosure you used? Does USB Type C work on the dock through your HP T3 dock?
 

Bremse

macrumors newbie
Jan 30, 2020
3
1
The dock is HP model HSTNN-CX01. This model is a flat slim brick with several USB ports and two Displayports (haven’t tried DP but USB works). You can find them on eBay for about $25 without the power adapter or about $50 with (power adapters alone are around $15-$50 as well so need to shop around a bit). Mine has a 150W power adapter but they have a 65W model as well that should be fine and might be cheaper.

HP also makes a bigger cubes shaped dock which seems to sell for a bit more. I haven’t tried that one but think it will work as well. That model has what appears to be an attached TB3 cable but the instructions say it can be removed although I’m not sure how much room there is for other TB3 plugs (the connector is under a cover). This would be fine if your TB3 Drive has a detachable cable but mine doesn’t. The Apple TB adapter has a TB3 connector so you need to have a female socket to connect it.

I haven’t tried USB-C (or 3.2). My dock has two C style sockets but I’m using them both for Thunderbolt (one for the adapter and the other for the drive). I don’t know if any of the USB type A ports support 3.2 or if they are just 3.1. When I tried an external USB3.1 ssd I got a little less speed via the dock compared to directly connected to the iMac (about 320 MB/s vs 350 with a Crucial MX500 1TB in an older cheap USB enclosure).

The TB3 SSD I have is a VisionTek 512GB that came already assembled as an external drive. I don’t know what brand or model the internal NVMe blade is but I assume it’s a lower end unit given the price. It was $99 but looks to be up to $105 now. Just search for VisionTek Thunderbolt SSD on Amazon. They also have a 1TB model for $180 (wasn’t available when I bought mine).
 
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