Helping a friend - older Imac - Booting from external SSD

Gary Goldblum wrote:

Hi,

I'm helping a friend who has a very slow Imac (https://everymac.com/systems/apple/imac/specs/imac-core-i5-2.8-21-inch-aluminum-late-2015-specs.html).I'm thinking his best (and cheapest) option is to buy an external SSD and install Monterey on it. I know ripping apart Imacs are not easy and apparently you cannot upgrade the RAM on this computer.

Looks like your friend was unfortunate enough to get one of the few 21.5" iMacs whose RAM is not only sealed in, but soldered in.

His Imac has 2 Thunderbolt 2 ports and I am wondering if there is a cable that goes from Thunderbolt 2 to USB-C.

There is no adapter from Thunderbolt 2 to generic USB-C (USB, DisplayPort, Thunderbolt).

Will this work? I'm thinking a Sans Disk...https://www.amazon.com/SanDisk-2TB-Extreme-Portable-SDSSDE81-2T00-G25/dp/B08GV9M64L/ref=sr_1_5?crid=33QOIXIVGMCEL&keywords=sandisk%2Bextreme%2Bpro&qid=1689087734&sprefix=sans%2Bdisk%2Caps%2C307&sr=8-5&ufe=app_do%3Aamzn1.fos.304cacc1-b508-45fb-a37f-a2c47c48c32f&th=1

That drive comes with USB-C and USB-A cables. That Mac has four USB-A (USB 3) ports. So you could plug the drive directly into one of the iMac's USB ports, instead of trying to use the Thunderbolt 2 port.

It is a USB 3.2 Gen 2x2 drive. USB 3.2 Gen 2x2 has a theoretical speed of "up to 20 Gbps", but I'm not sure if any Macs support that. I've seen reports that even Macs that support 40 Gbps Thunderbolt and USB4 40 Gbps mode do not, the result being that speeds fall back to a USB 3.1 Gen 2 common denominator.

There might be some sort of Thunderbolt dock arrangement that you could get for that old iMac which would give you a USB 3.1 Gen 2 port (USB-A or USB-C), but nobody makes Thunderbolt 2 docks any more, and connecting a Thunderbolt 3 dock via the $50 Apple TB3-to-2 adapter could get expensive.

So you could consider that drive – for use as a USB-A (USB 3.0) drive on the current Mac, with an eye towards the ability to use it as a USB-C (USB 3.1 Gen 2) drive on a newer Mac, in the future.

kaz-k wrote:

USB-C to Thunderbolt 2 adapter is available at online AppleStore and Amazon.

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?fnode=26adedf2ad8e0bbbb4629b496ce6385e545d0f4a4d754ad727edaf08d8372abef5a38d63f2fe2b0571b76fc08c38387ac5b932c8f48fa7e17eef83f616588fd7d3feb1cba5afa94a0563d087fa4f6069f8f3d8a79bec2757d8cc6b5240468fffd133de9a34983bd09e56c2fcc183850c&fs=f%3Dadapter%26fh%3D4595%252B45b0

That is not a USB-C to Thunderbolt 2 adapter. It is a Thunderbolt 3 to Thunderbolt 2 adapter. On the USB-C end, it requires a USB-C port that has Thunderbolt (not all do). And it only translates Thunderbolt protocol.

If you plug the Thunderbolt 3 end into a Mac's Thunderbolt 3/4 host port, the Thunderbolt 2 side of the adapter will not double as a Mini DisplayPort, the way that Thunderbolt 2 host ports on Macs did. The adapter does not do the work to extract any embedded DisplayPort signal.

Likewise, if you connect the Thunderbolt 2 end into a Mac's Thunderbolt 1/2 host port, I would not expect the Thunderbolt 3 end to start offering a full range of USB-C (USB, USB Power Delivery, DisplayPort) services (in addition to USB-C (Thunderbolt) service) just because the Thunderbolt 3 end has a USB-C connector.

There's no indication that the SanDisk SSD in question is a Thunderbolt device. So I would expect the use of the adapter in this way to fail.

Gary Goldblum wrote:

I would think that he would get better performance from the Tbolt. Is there any way to know which ones are compatible? Thanks everyone for the advice.

If money is no object, you could try getting a Thunderbolt 3 / M.2 PCIe NVMe SSD, and connecting it using the TB3-to-TB2 adapter. You can get these SSDs pre-assembled, or get the enclosure and a SSD separately.

You would want to get an enclosure that did not have a permanently-attached cable. (The TB3-to-TB2 adapter has a plug on the TB3 side, since it's normally plugged directly into a Mac's TB3/TB4 host port.)

Note that you would need to distinguish between enclosures that used Thunderbolt, and those that used USB, but that also had USB-C connectors. The USB-C (USB) enclosures are cheaper, and they might be advertised as being "Thunderbolt-compatible," but it's only the ones that use Thunderbolt protocol that you might be able to use with the TB3-to-TB2 adapter.

My feeling is that instead of getting a $50 TB3-to-2 cable, and a $100 TB3 enclosure into which to install a M.2 PCIe NVMe SSD (for additional $), you should just go with a USB / SATA SSD.

I ran my 21.5" late 2015 iMac on an external Samsung T7 for months. It made the machine a joy to use ... disk read speed went for about 90 MBps for the internal HDD to 450-480 MBps for the external SSD.

You're not going to get 2000 MBps out of the old Mac via USB-A ports; very likely not at all. TB2 usage is pretty much nil as it requires rather expensive gear to work. I think that situation may have changed in the last three years but still, TB2 is not really going to be a simple plug and play thing.

GUID partition map with APFS partition formatting should be used for SSDs with 10.13 and newer.

HPSF was the old standard used by 10.12 and older.

File system formats available in Disk Utility on Mac - Apple Support

1) The drive advertises "Thunderbolt 3" compatibility prominently.

2) The drive comes with a power adapter.

Unfortunately the only examples I can find are multi-drive enclosures intended for RAID setups which are probably expensive overkill. I've linked to two examples, but would still recommend USB.

Two examples:

https://www.amazon.com/Sabrent-Thunderbolt-Tool-Free-Enclosure-EC-T3DN/dp/B08S5JPWR6/ref=sr_1_3?crid=24B85NOZRWP3J (Enclosure only. Some DIY assembly to install M.2 SSDs purchased separately)

https://eshop.macsales.com/shop/owc-mercury-pro-u2-dual

USB-C to Thunderbolt 2 adapter is available at online AppleStore and Amazon.

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?fnode=26adedf2ad8e0bbbb4629b496ce6385e545d0f4a4d754ad727edaf08d8372abef5a38d63f2fe2b0571b76fc08c38387ac5b932c8f48fa7e17eef83f616588fd7d3feb1cba5afa94a0563d087fa4f6069f8f3d8a79bec2757d8cc6b5240468fffd133de9a34983bd09e56c2fcc183850c&fs=f%3Dadapter%26fh%3D4595%252B45b0

https://www.amazon.com/Apple-Thunderbolt-USB-C-Adapter/dp/B01MQ26QIY/ref=sr_1_6?keywords=thunderbolt+to+usb+c&qid=1689089094&sr=8-6

I'm not ku4hx but were I in your shoes, I would probably go with a USB3 external, as long as the SSD inside the USB enclosure is rated at SATA 6G. IMHO the T-bolt option is best applied to 2017 and newer iMacs because of their better T-bolt support.

Also the 2015 is already eight years old and cannot run a higher macOS than Monterey. The cost/benefit analysis for an older iMac like this favors the USB3 option. Put it this way: at best, your friend is getting file transfer rates from the current mech drive of, at most, 80MB/sec and likely less. The low-cost USB3 option should do 400MB/sec and, although a bit slower than the T-Bolt option, that will still feel like you got a new computer. And you can get a 500GB unit for US$70. Example:

https://eshop.macsales.com/item/OWC/MSU3SSD480GB/

You do not need as large an external drive as the current internal because you still have access to the internal for storage and other things that do not require speed.

The above drive has the option of a US$10 external power supply to make it a self-powered drive. I recommend that for desktop computers because self-powered drives are far more reliable, something important for a boot volume.

Yes, we recommend USB-A to USB-C. Such an external SSD should significantly improve performance.

TB2 -> USB 3.1/3.2 does not work (incompatible protocols). TB2->TB3 can work, but only for Thunderbolt certified peripherals which have their own external power supply. The Thunderbolt2 adapter does not supply bus power and will not work with bus powered TB3 devices.

If you can get TB2 to work, go for it.