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I'm planning to set up a FreeNAS box for home use, and would prefer to boot from a USB flash drive. The hardware I'm considering doesn't have USB 3.0, but I'm doubtful it would make a difference: once the OS loads into memory, will it need to read much off the USB drive? Other than the initial boot-up time (which I don't care about) is there any reason I would want to install a USB 3.0 card in it and use it for the boot drive.

(I'll probably install one for use with external platter drives anyway, but all I'm asking about in this question is how it would affect my boot drive.)

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migrated from Aug 14 '12 at 21:28

This question came from our site for system and network administrators.

Are you using it strictly for boot, or will there be any OS files on it? – Ignacio Vazquez-Abrams Aug 14 '12 at 21:31
I'm booting all the way from it, including loading the OS. So perhaps not strictly speaking just booting. But in the most common use of the word, I'm "booting" from it. – iconoclast Aug 15 '12 at 14:24
up vote 2 down vote accepted

Answer is very likely no.

I use Openmediavault and a few XBMC boxes (OpenELEC, raspbmc) from SD cards and tried different SD cards/flash drives/SSDs, the performance differs by boot time only. Once an application is started, it operates in RAM. It should be the same with FreeNAS.

Another story would be activity logging and other read/write activities which are performed while OS running (for example if you have MySQL plugin+MySQL installed).

Tolga Hoşgör: In real usage, maximum USB 2.0 transfer rate (with modern chipsets) is ~32MB/s, which could be a bottleneck for some very high speed drives. Usually only USB 3.0 or eSATA flash drives are limited in speed when connected to USB 2.0 connector, because pure USB 2.0 drives typically don't include memory chips faster than ~35MB/s.

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I'm not understanding your last sentence "(Usually only USB 3.0 or eSATA drives are limited in speed when connected to USB 2.0)". – iconoclast Aug 15 '12 at 14:49
Don't get confused, that was primarily targeted at Tolga Hoşgör and his "60MB/s statement" (in previous version of his answer). I was trying to say that USB 2.0 flash drives generally don't include memory chips faster than 35MB/s read/write. There's no reason to do so since it would increase the price and would have no effect at overall speed. – babca Aug 15 '12 at 19:16
USB 3.0 and eSATA flash drives typically use modern, faster and more expensive memory chips, which can take advantage of higher transfer rates of 3.0/eSATA. It is useful when using drive for user data (common files like documents, movies...), but it's not that important for minimalistic linux distros' system drives (like FreeNAS, OpenMediaVault or OpenELEC). Just stick with your 2.0 drive, no need to upgrade in your case. – babca Aug 15 '12 at 19:16

Well, the whole OS does not load into RAM as far as I know.

Anyhow, according to this, maximum USB 2.0 bandwidth is 60MB/s but no generic flash drive is close to that yet.

So, the answer is no, you will see no difference between USB 2.0 and 3.0 for flash drives.


As babca said, 60MB/s is theoretical speed of USB 2.0. In practice, it is around 30MB/s according to this. I have done some research and found that there are actually some flash drives that go beyond USB 2.0 speed. (did not know because none of them are sold in my country, and also all are too expensive yet)

Focusing back on your question, the answer is still no in my opinion. Because I don't think you will ever use the 32MB/s transfer rate for home use. (you should actually define that home use you said there).

I assume the maximum transfer rate you will need is watching a Blu-Ray film, unless you have a super duper over-240Mbit/sec internet connection bandwidth. Blu-Ray disc's read mechanism allows 4.5MB/s only, so I assume you will be able to watch quite fine.


You will see little to no benefit from USB 3.0 transfer rate for home use. Adding the over-price of USB 3.0 flash drives to the equation concludes that sticking to USB 2.0 is fine.

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Are you saying that in general (quite apart from the situation I'm describing) you'll see no difference between USB 2.0 and 3.0 drives? – iconoclast Aug 15 '12 at 14:49
No difference for flash drives at least. None of them use the full potential of USB 2.0. High speed SSDs and such can go beyond USB 2.0 speed of course. However I'll add a note to the post. – Etherealone Aug 15 '12 at 15:02
And yet in tests, USB 3.0 flash drives are pretty consistently faster. How does that fit into this picture? – iconoclast Aug 15 '12 at 15:37
I think it's a mistake to assume that any USB interface can actually achieve the theoretic speed maximum. AFAIK USB is usually painfully slow compared to its boasted limits. I don't have a url, but I've seen comparisons of real-world performance between USB 2.0 and Firewire, and it was tortoise and hare. USB 2.0's claimed speed is all marketing smoke and mirrors. – iconoclast Aug 15 '12 at 15:40
Thats why I said no usb flash drive will fill the USB 2.0 bandwidth. One of the links in the post after the edit probably includes that USB 2.0 - Firewire comparison you are talking about. However, I see some third party benchmarks show that there are actually really high-speed usb flash drives, but they cost too much. – Etherealone Aug 15 '12 at 15:45

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