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External USB 3 SSD - bottlenecks for random r/w?

MythicFrost

MythicFrost

macrumors 68040
Original poster
Mar 11, 2009
3,944
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Australia
Currently I have the 2013 27 iMac with a 1 TB 7200 RPM HDD. I can shell out $300 AUD for a Mercury On The Go Pro Thunderbolt enclosure for an SSD, or $50 for a (Mercury) USB 3 one.

In terms of latency, and random read/writes, is there any substantial downside to using an SSD over USB 3.0? The sequential speeds aren't important to me. Also will boot camp on Windows 10 work fine as well over USB?

Appreciate any input!

EDIT: In fact, I could even just get this SATA to USB 3.0 cable: http://www.warehouse1.com.au/epages/shop.sf/?ObjectPath=/Shops/warehouse1/Products/USB3S2SAT3CB

EDIT: 2 (Don't use warehouse1, they have the worst reviews I've ever seen in my life.)

And avoid needing an enclosure at all.
 
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I am using a iMac 5K 2014 late. I use a usb box with a 512G mx100 Crucial SSD. My external box is http://www.amazon.co.jp/センチュリー-シンプルBOX2-5-USB3-0-2-5インチSATA-HDDケース-CSS25U3BK6G/dp/B00BUGPO6S

This box is special design for SSD as it is only 7mm and very fast.

I am using it to install OS X 10.11 beta at that time and I should say it feels no difference from the inside SSD with OS X 10.10 on everyday usage. Also it is much cheaper than the box using thunderbolt.

At least, you should buy one with the fastest chip inside. As not all usb3-sata are equal speed.
 
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There is something called UASP which should make USB connections much faster. If Thunderbolt is to expensive I would choose an USB 3.0 enclosure that supports UASP, like that one for example:

http://www.amazon.com/dp/B00FCLG65U/

Does Amazon Australia only sell Kindle stuff? I took the US version, might be better to read for you than the german one where I found it first.

Just search for USB 3.0 UASP in a shop you buy usually.

I don't know if you can run Windows from an external drive since I don't use it. A read somewhere here that it does not work.
 
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MythicFrost said:
In terms of latency, and random read/writes, is there any substantial downside to using an SSD over USB 3.0?
Click to expand...

Very little difference. See this test. Unless you are a pro user where every last second matters and money is not an issue, I see little reason to spend the extra money for TB on a consumer drive.

Make sure you get a USB3 enclosure that supports UASP like Erdbeertorte mentioned. I have the drive he linked ($15 on Amazon) and it works well.

The only downside to USB3 is it does not support TRIM with an SSD, where TB does. All new SSDs have built in garbage collection anyway, so I would not be concerned about this for your usage.
 
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Agree with above. I use both Thunderbolt and usb3. No idea about speeds but certainly nothing that's noticeable to me. Perhaps on long sequentials Thunderbolt might have an edge, if the process is limited read or write. TRIM is desirable to me. My usb3 externals get the hand-me-down ssd's after I upgrade for added space.

Re UASP: practically any USB chipset uses it these days, whether they mention it in the specs or not. Some refer to it as Hi-Speed, some USAP, some don't call it out at all. Check the chipsets if it's important to you. OWC's are all USAP. They didn't used to make a big deal out of it to the point of not mentioning it their specs. Haven't looked for a while.

The linked drive from Amazon in the Far East looks very much like OWC's Express series. That's what I use. Cheap and good. Not sure which enclosure you're looking at for $50 but the Pro Mini's are quite large if you plan to travel with them. At the time I made my purchase, they all used the same chipset.
 
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Thanks guys! Appreciate all the input. I ended up ordering the Transcend enclosure, as it looked to be just as good if not better than the OWC one.
 
Weaselboy said:
The only downside to USB3 is it does not support TRIM with an SSD, where TB does. All new SSDs have built in garbage collection anyway, so I would not be concerned about this for your usage.
Click to expand...

I've had this with a SAMSUNG 470 SSD and the GC only was not enough. This is what I've learned ... The SSD becomes horrible slow after ±one year.

I could fix it with an Time Machine backup - > Format the drive in Windows and -> restore the backup.
But maybe the todays GC are much better. At work we got FusionIO Cards which don't need TRIM either but they are really expensive.

If someone is interested:
http://arstechnica.com/gadgets/2015...garbage-collection-so-i-dont-need-trim-right/
 
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OP:

DO NOT buy ANY USB3 enclosure, dock, or dongle UNLESS it is specifically stated that it has UASP support (USB attached SCSI protocol). You need this in order to get the highest speeds of which USB3 is capable.

That said, I don't see any reason to spend two or three times as much in order to get a thunderbolt enclosure, when USB3 will be nearly as fast (not the "equal", but very close).

The right USB3 enclosure or adapter will yield read speeds around 420-430mbps and writes around 330mbps.

Unless you are moving mountains of data, I predict you'll be quite satisfied with these speeds...
 
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Thanks for your help everyone.

I bought the Transcend StoreJet 25S3. It has UASP support.

I installed 10.11 on an old Crucial M4 64GB SSD I had around. I'm trying to verify that it's running on UASP.

According to this post IOUSBAttachedSCSI is now IOUSBMassStorageUASDriver in El Capitan. I do see this when I look the IOReg output, and half a dozen lines underneath it is the StoreJet Transcend. So I'm pretty sure it's working.

I did a run of XBench to see what speeds I'm getting:

The results were:

Sequential 162.42
Uncached Write 188.39 115.67 MB/sec [4K blocks]
Uncached Write 169.93 96.15 MB/sec [256K blocks]
Uncached Read 84.41 24.70 MB/sec [4K blocks]
Uncached Read 629.81 316.54 MB/sec [256K blocks]
Random 732.07
Uncached Write 835.50 88.45 MB/sec [4K blocks]
Uncached Write 324.87 104.00 MB/sec [256K blocks]
Uncached Read 2103.92 14.91 MB/sec [4K blocks]
Uncached Read 1401.29 260.02 MB/sec [256K blocks]

That looks like the correct speeds to me for the 64GB model, but I thought I'd post them just in case.

Curious why Uncached Read (4k Blocks) is so low in Sequential and Random. It's normal from what I've seen, but interesting nonetheless. My HDD beats it.

Appreciate all the info!
 
MythicFrost said:
Thanks for your help everyone.

I bought the Transcend StoreJet 25S3. It has UASP support.

I installed 10.11 on an old Crucial M4 64GB SSD I had around. I'm trying to verify that it's running on UASP.

According to this post IOUSBAttachedSCSI is now IOUSBMassStorageUASDriver in El Capitan. I do see this when I look the IOReg output, and half a dozen lines underneath it is the StoreJet Transcend. So I'm pretty sure it's working.

I did a run of XBench to see what speeds I'm getting:

The results were:

Sequential 162.42
Uncached Write 188.39 115.67 MB/sec [4K blocks]
Uncached Write 169.93 96.15 MB/sec [256K blocks]
Uncached Read 84.41 24.70 MB/sec [4K blocks]
Uncached Read 629.81 316.54 MB/sec [256K blocks]
Random 732.07
Uncached Write 835.50 88.45 MB/sec [4K blocks]
Uncached Write 324.87 104.00 MB/sec [256K blocks]
Uncached Read 2103.92 14.91 MB/sec [4K blocks]
Uncached Read 1401.29 260.02 MB/sec [256K blocks]

That looks like the correct speeds to me for the 64GB model, but I thought I'd post them just in case.

Curious why Uncached Read (4k Blocks) is so low in Sequential and Random. It's normal from what I've seen, but interesting nonetheless. My HDD beats it.

Appreciate all the info!
Click to expand...

Looks pretty good to me. As for the 4K read, I think spinners are always faster than SSDs when it comes to small reads and SSDs beat them in larger files. Not sure why. Probably something to do with the way data is written to the drive.
 
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