LaCie SSD as Boot Drive for 2012 iMac

Discussion in 'iMac' started by lawhochun, Jun 23, 2013.

  1. lawhochun macrumors member

    Oct 24, 2012
    Hong Kong
    I know there have been several posts about booting imac from external SSDs. Recently I have been doing some research on which external SSD to get, and it seems like the LaCie Rugged SSD Thunderbolt is the safest option. However, i also came across LaCie Porsche Design P'9223 Slim USB 3.0 120GB Solid State Drive - it is US$50 cheaper than the Rugged but with no Thunderbolt. Does thunderbolt really matter given USB3 has pretty much similar read/write speed. Has anybody tried this?

    Any thoughts?

    Thank you!
  2. Radiating macrumors 65816

    Dec 29, 2011
    I don't think you can set a USB 3.0 device as a default boot device.
  3. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    There is a test here showing exactly what you are after. Excerpt below from the test.



    It will work.
  4. g4cube macrumors 6502a

    Apr 22, 2003
    As long as you have an Apple Partition Map, or GPT/GUID partition map, you will be able to boot from a USB 3.0 hard drive, even on a USB 2.0 equipped Mac.

    You can't boot from an MBR partitioned drive. All of these partition options are within the Options of Disk Utility after you select the top level hard drive, and the Partition Tab.

    I have a partitioned USB 3.0 SSD drive (yes, both a Porsche, as well as the combo Rugged), with different versions of OS X installed for testing.

    You can use Startup Disk to select the default volume to boot from, or the "press Option key during startup" method to select the OS X volume to boot from.

    This also works with USB 3.0 thumb drives.
  5. Nuke61 macrumors 6502

    Jan 18, 2013
    Columbia, SC
    The only advantage that Thunderbolt has, and it's arguable whether it's even needed anymore, is that it supports the TRIM command and USB 3.0 doesn't. Why I say it's arguable whether it's needed is because most/all current SSDs do their own unused block cleanup routines.
  6. g4cube macrumors 6502a

    Apr 22, 2003

    I think there is unwarranted attention to the need for TRIM in modern SSDs.

    This was a seed planted years ago, and too many are focusing on enabling it when upgrading their computers.

    Better to focus on reliability and utility. It's not like anyone will be constantly running benchmarks, now, will they?

    I don't bother with TRIM on my external SSD drives. Then again, all current technology, too.

    Perhaps someone like Anand at Anandtech might shed some light on this in a more comprehensive, up-to-date look at current controllers.
  7. Fishrrman, Jun 24, 2013
    Last edited: Jun 24, 2013

    Fishrrman macrumors G5


    Feb 20, 2009
    "I don't think you can set a USB 3.0 device as a default boot device."

    This is incorrect.

    A USB3 external drive (or a USB3/SATA docking station) will make an excellent "external booter".

    I use a "lay flat" USB3/SATA dock in conjunction with an Intel 520 series SSD to but and run my 2012 Mac Mini -- very fast, very solid, completely reliable.
  8. lawhochun thread starter macrumors member

    Oct 24, 2012
    Hong Kong
    Thank you all for your very helpful responses! I guess I will go for the myself a little cash.
  9. Chippy99 macrumors 6502a

    Apr 28, 2012
    Sorry to cut in, but no SSD's can perform optimally without being sent a TRIM command. Without TRIM they have no way of knowing what data is deleted and they do garbage collection on deleted as well as current data. The SSD thinks it is much more full than it really is and does much more background reading and writing and it slows down quicker and wears out quicker.

    Contrary to what 90% of people seem to think, background garbage collection is NOT a substitute for TRIM. All SSD's do their own garbage collection and have been doing so for years. This is not a feature of modern SSD's only.
  10. iamgalactic macrumors regular

    Apr 21, 2010
    Yeah, that test isn't exactly a good comparison. The Lacie although Raid 0 and using 6Gbps SSDs is slightly hobbled by the fact the SATA controller is split in 2 - so the speed on each drive will be 3 Gigabit . Whereas they're comparing two miniSWAPs - using 2 SATA controllers giving 6 Gigabits on each drive.

    An accurate test would be to use 2x lacie rugged thunderbolt ssds (for example).
  11. Nuke61, Jun 28, 2013
    Last edited: Jun 28, 2013

    Nuke61 macrumors 6502

    Jan 18, 2013
    Columbia, SC
    I haven't read enough about TRIM vs garbage collection to add anything to the discussion about whether it's needed or not - and given that I didn't know, that's why my external boot SSD is via Thunderbolt:D

    O.K., I did a search for an article about GC and Trim. It details what you've said, which is that GC isn't a substitute for Trim. Additionally, Sandforce controllers are better if you can't do Trim, but even with them, having Trim is the best option.
  12. Chippy99 macrumors 6502a

    Apr 28, 2012
    Absolutely correct. Without Trim, the SSD has no way of knowing what data has been deleted.

    Imagine working on a 10MB Powerpoint presentation (I do all the time!) PowerPoint will do background saves every 5 minutes. Over the course of a day's work that means PowerPoint will write perhaps 1200MB of data to the SSD. The SSD will juggle around 1200MB of data trying to keep it all neatly arranged to maximise the amount of empty free space. But 1200MB is tied up, when in fact it should only be 10MB. There's 1190MB of deleted data that the SSD does not know has been deleted.

    That is what happens without Trim.
  13. g4cube, Jun 28, 2013
    Last edited: Jun 28, 2013

    g4cube macrumors 6502a

    Apr 22, 2003
    The lack of TRIM only slows down the writes after the SSD nears getting full.

    OS will always write to what it thinks is free space, until it reaches the end of the logical drive. Files that the OS know are erased are not always written to first.

    So, if your SSD is barely filled, the OS is writing to true empty space that has never been written to.

    Once a drive is nearly full, then the previously areas marked as erased are written to, leading to fragmented files.

    That being said, if you are going to be constantly running benchmarks to see the performance of your drive, then having TRIM support is important. Otherwise your SSD will still be quite speedy. The SSD will do a read-modify-write of a block unless it knows that the block does not have real file info within the block. The TRIM function as implemented by the OS, tells the SSD controller which blocks are supposed to be empty - i.e. blocks that the OS knows are no longer part of files.

    So the time saved is the SSD is able to do direct writes to a block of storage rather than a read-modify-write.

    By the way, bunches of refurb 1TB HDD Rugged Thunderbolt/USB3.0 and desktop 3TB d2 Thunderbolt/USB3 drives at MacMall at low prices today.
  14. Chippy99 macrumors 6502a

    Apr 28, 2012
    Whilst this is true, it is also misleading because you don't specify full of what?

    As you go on to describe, without Trim, old deleted data is indistiguishable from fresh live data as far as the SSD is concerned.

    So you could look at your 128GB SSD and it might appear to only have say 50GB on it (because that's what the OS can see as live data), and yet it is still full as far as the SSD is conccerned because there's another 78GB of old deleted data on there that the OS knows is deleted, but the SSD does not.
  15. g4cube macrumors 6502a

    Apr 22, 2003
    Thanks for extending my comments, as that is what I was trying to say. While the OS will think the SSD is partially full, the SSD will have files that may have been deleted, but does not know what blocks should be preserved, and what blocks could be erased. In this case the OS simply tells the SSD to write particular blocks, and the SSD has no idea that the blocks have been marked as already erased.

    So, a read-modify-write must be performed, instead of a simpler, faster write.

    That being said, TRIM could cause some blocks to be written more frequently, and the SSD still must take precautions to prevent this write amplification.

    What is good for SSD longevity is making sure that blocks are written to less frequently, so spreading the writes over the entire SSD is what works out best in the long-term.

    Over time, each new generation of SSD controller makes compromises to balance performance with longevity. There still is a very large max number of writes that each physical block can endure. There are many articles discussing this with extensive math computations to predict the useful life of an SSD. The job of the controller is to manage these writes over the entire SSD.
  16. Chippy99 macrumors 6502a

    Apr 28, 2012
    And thanks for extending mine from post #9 ;-)

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