Extnal SSD as Boot Drive

Discussion in 'Buying Tips and Advice' started by North East Loon, Feb 3, 2019.

  1. North East Loon macrumors newbie

    Feb 3, 2019
    I run a late 2013 27” i5 standard iMac with a 7200 rpm. HDD and am considering the option of an SSD as an external boot drive.

    Everything I read on MacRumors suggests there would be a dramatic performance improvement if installed internally, but, I do not want to go down this route.

    So, my questions are:

    a)Would external cabling cancel-out any improvement I would see if installed internally?

    b) If there was any improvement to be gained by installing externally, would this be worth the investment, or, be marginal

    c) Would I be better using Thunderbolt or USB on my machine.

    Thank you in advance for any advice received.
  2. casperes1996 macrumors 68040


    Jan 26, 2014
    Horsens, Denmark
    Isn't this essentially the same as question b?

    Well, I just so happen to run an external SSD on my iMac. It has an internal Fusion Drive, and right now I don't boot from the external, but only use it for storage, but I have used it to test beta versions in the past.
    I'd say the latency is higher than an internal drive, but the bandwidth isn't really that different. This is over USB 3.0. Thunderbolt has lower latency.
    Boot up speeds aren't as good - I think the way the iMac POSTs, it may initialise HDD/SSD first to start booting before having initialised external busses to speed it up. That's just a guess though based on how booting seemed to be a much greater speed difference than I otherwise observed. Still a lot faster using the external SSD than an HDD. I personally don't think it's worth the hassle opening up an iMac to make it internal.

    Thunderbolt is like a PCIe x4 link (With TB2 that's a PCIe 2.0 link). This means lower latency and the potential for higher bandwidth and more direct communication between the computer and the drive, including less overhead from the USB protocol. An external Thunderbolt drive can beat an internal SATA drive. So the upsides are plentiful. The downside is price. So it mostly comes down to what you're willing to spend.
  3. North East Loon thread starter macrumors newbie

    Feb 3, 2019
    Casperes1996, I am of a certain age, over 70 that is, and, I am old enough to remember the old hi-fi separates rule, which is, there is no point in just upgrading one component as the system is only as strong as the weakest element.

    Price is a factor, and, it would be heart-breaking if I invested in a quality external SSD and possible enclosure, only to find that it is fighting the faster internal wiring.

    Thank you for your comment, I may just soldier on, and, if I'm still around when the machine gives up the ghost in a few years time, buy a new iMac and take advantage of the improvements in technology.

    Have a good day!
  4. casperes1996 macrumors 68040


    Jan 26, 2014
    Horsens, Denmark

    Well, the benefit of getting the external drive, is that you can bring it with you to your next computer. You may need a new cable for it, but the drive will be as good as always.

    Your phrasing of the bottlenecking issue is a bit off I think. There would be no "fight" with the internal components. When the CPU issues a request for IO, it would issue the request to the external SSD and never cross paths with the internal drive or its connection. Since the internal drive is a spinning platter and the external is an SSD, the request would be finished faster on the external, and thus you'd have less bottlenecking, and the CPU would be waiting less for the data. Whilst it'll overall wait less, it may however take longer before the drive starts looking for the data, because the connection adds a bit of latency for the drive to get the request, but since the overall return time would still be faster, you'd gain performance.

    Plus, computing isn't entirely like hi-fi. In hi-fi your goal is to get good audio. If your pre-amp gives a bad signal, your amp will only amplify the bad signal. If your amp gives a bad signal, your speakers will produce a bad signal. If your needle on your vinyl player is low quality it'll give a bad signal - all the pieces always combine to create the end result.

    Computing is a bit different. Some tasks only require some components, and put various levels of strain on each component. If you work with bandwidth limitted IO tasks a lot, an external SSD will make a massive improvement, regardless of other elements of your system. If you work with latency sensitive IO, it'll still make a difference, but the connection method will also have a big impact - in any case it's better than a spinning platter disk. - If you don't work with IO tasks at all, you'll literally see 0 difference whatsoever. Typically computing does depend on a decent amount of reads though; For loading things that's typically sequential and for various system level functions it's smaller chunks of data randomly split across the disk - a library here a framework there, all serving various utilities.

    The decision is all up to you, but I'd like you to have as much information to make it as possible :)

    PS. I'm into hi-fi myself ;). And am also a computer science student so that's a bit of ethos if need be, hehe

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