Connecting Linux on an External Drive: USB? eSATA? Firewire? SSD?

As described in another post, I was thinking about running Linux, and a Windows 7 virtual machine (VM), from an external drive. I knew that an internal solid state drive (SSD) would be faster than an internal hard disk drive (HDD), assuming both were using standard SATA cabling. I was not sure which kind of cabling would be best for an external drive, nor whether the cabling would reduce the performance difference between external SSD and HDD drives.

Ultimately, I decided not to pursue this external route. I have preserved my notes for reference nonetheless, in the incomplete form set forth below.

Eliminating Some Possibilities

I was able to rule out some options pretty quickly. First, Firewire was developed by Apple, not widely present on PCs, and apparently being abandoned by Apple as well. Neither my laptop and desktop computers nor my external drive docks had Firewire ports. So that was not a realistic option. Also, I was not sure if Ethernet was an option for a bootable drive. If it was, it did not emerge as such during my browsing, nor from the top results from a search to that effect. In addition, I saw that some hardware was advertising USB 3.1 and SATA Gen 2 (10Gbps) capability, but my computers’ drives and ports were limited to SATA III and USB 3.0.

Of course, there was the option of running a live CD (or DVD, USB flash drive, SDHC card, or other bootable version of the preferred Linux system). To boot from such a device, the computer’s BIOS or UEFI settings might have to be adjusted. Then the computer would look at that device, rather than at the internal drive, for its bootup instructions. As discussed in a previous post, such a device could actually contain multiple operating systems and tools, with a menu allowing the user to choose which one s/he wished to boot. A live CD would have speed problems, as the operating system slowly looked for needed instructions or information on the spinning CD. In addition, a live CD (or non-rewritable DVD or Blu-ray disc) could not be configured, except perhaps through a cumbersome process of customization and re-burning. That is, changes made during a session would not persist after logoff.

With at least some Linux distributions, a live USB or SD/SDHC memory device could be set up to preserve space to remember changes in configuration, and would also be faster than a CD/DVD. But such devices were not typically built to endure the wear that a system drive would experience, and it was not clear whether they would necessarily be as fast as an HDD. I decided not to pursue these flash memory options. I did notice, however, that there could be considerable performance variations among such devices. For example, I observed that Griffin (2015) found significant speed differences between Lexar and V.Top UHS-II memory card readers.

Ruling Out eSATA

For the reasons cited above, it came down to a choice between HDD and SSD. There were different ways to connect such drives to a computer. I could have used a self-contained external drive, such as the Western Digital Passport, but I preferred the approach of buying an internal drive and putting it into an external drive dock or enclosure. That would be less expensive, and would give me more flexibility: I could use the same dock with different internal drives for different purposes; I could mount the internal drive inside the computer, temporarily or permanently, if needed; it was possible to buy external enclosures with fans and metal housings, if the drive seemed likely to be under a heavy load; and some external docks or enclosures came with more than one type of connector.

The specific external dock I chose was the Orico 6619SUS3, which emerged in a search at Newegg and drew an average of 4.3 stars from numerous users on Amazon. The Orico had both USB 3.0 and eSATA ports, facilitating (I hoped) something of an apples-to-apples comparison between those two interfaces. In the interests of avoiding data corruption or loss, the maximum recommended eSATA cable length was about six feet, but I noticed that many commenters advised no more than one meter (~3 feet), and the Orico unit itself shipped with a three-foot eSATA cable.

Once I received the Orico unit and put it to work, it turned out that eSATA, too, was not a contender. For those who may be considering this or other units, I will describe the factors that came into play. First, as with the experience of at least one user on Amazon, it appeared the Orico unit’s eSATA connector was not working. It was possible that the problem was with the eSATA connector on the computer — but I belatedly realized that that, too, was problematic, insofar as the connector was on the front of the machine, right next to the USB and headphone ports and above the CD drive, and as such would be vulnerable to bumps and accidental disconnection, any of which would be fatal for an externally housed operating system. I could have added SATA III ports to the rear of the computer, at a cost of $25, or I might have tried a SATA-to-eSATA adapter ($9) running straight from the motherboard to the external dock; and I could also have bought an adapter (for another $21) that would have given the laptop an eSATA connection through its ExpressCard port.

But there were more problems. Upon closer examination, it appeared that the Orico unit was not SATA III, which meant that the eSATA plan was dead in any event, as USB 3.0 would be faster than SATA II. The Amazon ad claimed SATA III capability, and so did some others, but then I saw there was no such claim in the fine print of the Newegg ad, and an Orico representative admitted, in response to an Amazon user question, that in fact the internal interface (i.e., where the drive plugged into the dock) was only SATA II. This implicated Orico in another falsehood, insofar as its Amazon ad claimed “data transfer rates of up to 5Gbps,” which would be possible through the USB 3.0 connector — but not when the disk-to-dock connector was only SATA II. It appeared the USB 3.0 connector on back of the Orico unit was just for show. For that matter, I wasn’t sure whether the ExpressCard solution (or any other adapter) for the laptop would be more than SATA II, if that.

I did have the option of buying a replacement for the Orico. My searches on Amazon and Newegg led to only a few devices offering eSATA capability, however, and in most cases the eSATA being offered was not the “eSATA version of SATA 6G” (using Wikipedia‘s allegedly preferred term for SATA III). Both the StarTech SuperSpeed ($43) and an Anker unit ($36) offered an eSATA transfer rate not exceeding 3 Gbps — that is, SATA II speed. The only real contender I found at a reasonable price was the StarTech SDOCKU33EF ($56), whose ad said it “supports full SATA III bandwidth of 6 Gbps when connected through eSATA.”

To recap, the situation appeared to be as follows. I wanted to compare the performance of Linux on an external as distinct from internal drive, with a further comparison on the external drive between USB 3.0 and eSATA III connections. If I bought that $56 StarTech unit and a $25 SATA III card for the rear of the computer, it appeared the external drive would perform about the same as if it were mounted internally. In that case, why not just mount it internally in the desktop computer? After all, I was not going to be able to get eSATA III performance out of the old laptop: it had no suitable connections, and it appeared none could be created. There would be no reason to mount an internal Linux drive externally, so as to share it among computers, if only one computer was capable of connecting to it effectively.

In any case, it was not clear whether eSATA would be necessary or even helpful. Various reports seemed to indicate that eSATA was not necessarily faster than USB 3.0, was more problematic, and was not available on as many computers. So probably a simple USB 3.0 external dock would be sufficient. It was certainly possible that an eSATA III connection would not result in performance as fast as that of an internally connected SATA III drive. Differences in that case could be due to the quality of the external dock. I might want to know that, if it appeared that the portable Linux HDD or SSD was viable otherwise. At this point, however, I suspected that the real break point had to do with the USB 2.0 connection to the laptop. Thus I decided at least to postpone further consideration of eSATA.

Other Considerations

Multiple sources agreed that the speed of a solid state drive (SSD) would be wasted in an external dock, due to the practical (as distinct from theoretical) speeds achieved via USB 3.0 or eSATA cabling. Sources were also unsure of whether the TRIM function (necessary for proper SSD self-maintenance) would work on an SSD mounted externally: apparently not, via USB, but perhaps not even if connected via eSATA.

If I decided nevertheless to compare the performance of an externally mounted HDD and SSD, I would have to choose an HDD and an SSD to test. Given the complexities of booting drives larger than 2TB, my search for an HDD pointed toward a highly rated Western Digital WD10EZEX 1TB drive. But I decided not to buy one: I had, on hand, a lightly used 1TB HGST 7K1000 (SATA III, 7200 RPM, 32MB cache, ranked 112 out of 940 at UserBenchmark), and I used that. For an SSD, meanwhile, the first question was how much space I needed. Ultimately, I planned to run virtual machines (VMs) on the system. In light of reports (1 2 3) indicating that running a VM from an external HDD could be somewhat or perhaps extremely slow, it seemed that I would probably wind up wanting to run both the operating system (OS) and its VMs from an internal or external SSD. Given the potentially large size of Windows OS installations, it appeared I would be best advised to choose an SSD of more than 120GB. My search led to the PNY SSD7CS1311-240-RB ($60, SATA III, 240GB, ranked 281/750 at UserBenchmark), as a decent alternative to the dominant Samsung 850 EVO ($88, 250GB, ranked 40/750).

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