iMac 21.5 Retina with SSD Question

Discussion in 'iMac' started by KS1990, Aug 17, 2016.

  1. KS1990 macrumors newbie

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    Aug 17, 2016
    #1
    Hello,

    I ordered an iMac 21.5" Retina with a 512 GB flash storage (SSD). On the box however I found that it was a simple 1 TB HDD 5200rpm. So I called them right away before unboxing the iMac. They said the drive was replaced by the authorized Apple dealer to SSD and it turns out that it really was. But...Here is my question.

    When I check the info about this iMac (About This Mac --> System Report --> Storage from the navigation), I see that there's a Samsung SSD indeed, but the protocol is SATA, not PCI. In my Macbook Pro retina I see the protocol is PCI. I have attached an image. Anyone with SSD (flash) storage can please check what they have there? Is this SATA in any way affecting the speed (such as booting up, etc) of my iMac? Thanks

    [​IMG]
     
  2. tubeexperience macrumors 68030

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    Feb 17, 2016
    #2
    We have upgraded quite a few Slim Unibody iMac(s) with SATA-based SSDs.

    They work great and are much much cheaper than the BTO option from Apple.
     
  3. KS1990 thread starter macrumors newbie

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    Aug 17, 2016
    #3
    My iMac is "iMac (Retina 4K, 21.5-inch, Late 2015)".

    I wonder if those who order SSD option (flash storage) has PCI or PCIe protocol in the system report instead of SATA. Please, can anyone check on this?

    And if they had a PCI protocol instead of SATA, would it mean that SATA doesn't use the full potential of my SSD? Is my iMac booting up slower?

    By the way, I also noticed that booting up time is quite faster after restart than after full shut down.

    Just trying to figure out I'm using the full benefits of my SSD drive! Thanks :)
     
  4. tyche macrumors 6502

    Joined:
    Jul 30, 2010
    #4
    Use a disk benchmarker like BlackMagic to check your speeds. I get the feeling you were short changed. You will see max SSD speeds but they are slower than pcie based storage which iMac use factory installed. Instead you got a 5400 platter drive system with the drive pulled and a aftermarket SSD installed like end users do to upgrade their machines after purchase.
     
  5. tubeexperience, Aug 17, 2016
    Last edited: Aug 17, 2016
  6. mpe, Aug 17, 2016
    Last edited: Aug 17, 2016

    mpe macrumors regular

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    Sep 3, 2010
    #6
    Looks like your iMac has been aftermarket upgraded by whoever you bought it from.

    Yes, it will be slower than the factory installed PCIe SSD, but depending on what you do the difference might not be significant. It estimate it'll be roughly two times slower that the factory unit, but still quite fast.

    If you saved good money compared to the stock 512GB iMac ($1999 model) then it was a good deal. I would personally have preferred a stock fusion or PCIe SSD over this.
     
  7. tubeexperience macrumors 68030

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    Feb 17, 2016
    #7
    lol, no.

    The fusion is worse.
     
  8. mpe, Aug 17, 2016
    Last edited: Aug 17, 2016

    mpe macrumors regular

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    Sep 3, 2010
    #8
    No. The SSD portion of 2TB/3TB fusion is pcie connected (same as standalone SSD pcie blades up to 512GB). In vast majority of situations it will be faster than SATA based SSD. Pretty much all writes under certain threshold and most reads go to SSD under normal use depending on how you use the volume.

    Surprisingly 24GB SSD in 1TB fusion (and 1TB SSD in 27" model only) is NVMExpress connected which is even faster than the standard 4 link pcie. However only 24GB of capacity makes it actually worse as read hit ratio is lower than when using 128GB portion of 2TB/3TB fusion.
     
  9. tubeexperience macrumors 68030

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    Feb 17, 2016
    #9
    The only Mac that uses NVME right now is the Retina MacBook.

    Also, sure the SSD part of the fusion is fast, but once that is exhausted, it's much slower.
     
  10. mpe macrumors regular

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    Sep 3, 2010
    #10
    That isn't correct. Factory installed 1TB SSD option in 2015 27" iMac is NVME and so is the 24GB SSD blade in 2015 1TB Fusion drives in all iMacs. You can easily check it out by checking system report :)

    Fusion drive isn't slower when exhausted. Or better said it is complicated as the Core Storage driver prevents it from being filled by demoting data to HDD. You probably wanted to say that once you have more than 128GB o your fusion drive volume it really depends on the traffic profile and the size of transfers. All writes under 8GB go to SSD and reads depend on whether data are on HDD or SSD. In fact it is the SSD that slow downs dramatically when filled up due to write amplification problem. Fusion drive prevents that problem by never allowing the SSD drive to fill completely.

    I've done really extensive testing of various Fusion drives against SSD and it is not as clear as it seems. Fusion drive is a very clever tech that gives you SSD performance and large capacity unless you have a very specific use case
     
  11. maflynn Moderator

    maflynn

    Staff Member

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    Boston
    #11
    I have a 2015 5k iMac running the latest chipset and I don't see anything about NVMExpress unless I'm reading it wrong:
    Capto_Capture 2016-08-18_06-42-01_AM.png

    Capto_Capture 2016-08-18_06-42-36_AM.png
     
  12. Samuelsan2001, Aug 18, 2016
    Last edited: Aug 18, 2016

    Samuelsan2001 macrumors 604

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    Oct 24, 2013
    #12
    Yes but you have a 2Tb fusion drive not a 1TB one, this is the claim of mpe. I don' have a 1TB fusion Mac for me 2015 to check their claims though.
     
  13. maflynn Moderator

    maflynn

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    #13
    I've heard the same thing being claimed for the 2TB Fusion drive tbe.
     
  14. tubeexperience macrumors 68030

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    #14
    I am unable to neither confirm nor deny that since I have no access to such an iMac. So, I will leave it at that.

    You are going to have a hard time arguing that having a Fusion Drive (SSD + hard drive) is faster having purely a SSD because it's not true.
     
  15. mpe macrumors regular

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    Sep 3, 2010
    #15
    Yes, FD could be faster than pure SSD. 2 TB Fusion can be easily faster than 500MB pure SSD Samsung 850-based solution.

    The logical error you are making is that you consider Fusion drive as a technology equal to magnetic HDD or SSD. Is your car faster than my car and bike?

    Fusion drive is in fact both SSD and HDD at the same time. There are two physical drives and the LVM software on top making decisions about which one should be used for particular request.

    So it doesn’t make quite to claim that FD is slower or faster than SSD or HDD. It can be both slower or faster or same speed depending on circumstances. Filled-up SSD that runs out of over-provisioned space might have terrible performance, SATA-connected SSD can be two times or so slower than PCIe, specific traffic profile can destroy performance of FD, fragmentation can hurt HDD, etc...

    It is more like a tech comparable to RAID. Its performance and comparison depends on which exact drives you fuse together and how exactly you use it.
     
  16. cynics macrumors G4

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    Jan 8, 2012
    #16
    OP, where did you buy the Mac from? And how much did you pay?

    Apple has a set price so it's not uncommon for 3rd parties to order a HDD iMac, swap in a cheaper SSD and sell it too you for a close to full retail thus making a profit.

    It's a shady way of doing business.

    SATA based SSD is fine but not at a PCIe price point. That's something you could do or have someone do for you cheaper.
     
  17. tubeexperience macrumors 68030

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    #17
    I'll use your analogy then. A fusion drive is like a car that can only go for 60 miles. If you drive less than 60 miles, you're fine. If you have to go further than that, once that 60 miles is up, you'll have to bike the rest of your way.

    A SSD is like a car that can go for 600 miles.
    --- Post Merged, Aug 18, 2016 ---
    He/she should have used a cheaper SSD to make an ever bigger profit. :D
     
  18. mpe macrumors regular

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    Sep 3, 2010
    #18
    Exactly :) It really depends how far you need to drive doesn't it? If using it to commuting 20 miles, like many people do, then the 60 miles car does exactly the trick. Especially if, unlike the 600miles two-seater car, can not only carry you but also your family, three dogs and all your friends.

    If you have >200GB of unindexed data files to search through every day or continuously cut gigabytes of uncompressed video files, then the 128GB+2TB FD isn't the best option. However, chances are that most people don't need that and 2/3TB FD is giving them exactly SSD performance (not less) and high capacity at the same time. Very few people actually need 100% consistent random access on top of >128GB of data or faster sequential writes beyond 8GB boundary...
     
  19. maflynn Moderator

    maflynn

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    #19
    I never heard that Fusion can be faster then a pure SSD, even apple would not make such a claim. It doesn't take much to full up a 128GB SSD (especially when you remove 30GB of space for he recovery partition), so odds are high that there will be data blocks on the spinning drive. No matter how you slice it, the hard drive will be slower.
     
  20. mpe macrumors regular

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    #20
    Not sure what are you talking about when mentioning the 30GB recovery partition. Recovery partition on OSX has roughly 650M and is located at the end of HDD volume of the Fusion. In addition to that OSX eats about 120M for boot partition + 200 MB for EFI purposes on every drive. The rest is managed by Core Storage. You probably meant a part of storage dedicated to over provisioning or write buffer zone?

    No it indeed doesn’t take much to fill 128GB. But it is actually not as easy either as requests > 8GB go to the HDD by default and core storage will do utmost to make sure that SSD remains available. It doesn’t matter how much data you have but how much you actually use and how big your transfers are. The chances are that most people will never notice any difference during normal use. But some people do have specific requirements and they should go for pure SSD.

    It is actually not that common to be using more than 120GB of data at the time to be impacted by HDD latency unless talking about very specific scenarios. Most people with data are using something like gigabytes of app data + hundreds of gigs of media files and the fusion drive excels at managing this and delivering SSD performance most of the time.

    And yes it is easy that 8 GT/s pcie 4x chips in 128GB SSD blade in Fusion drive can easily beat SATA-connected 850-series EVO drive as it has 2 times throughput in both reads/writes. Unless exceeding the threshold, obviously. I am also not aware if Apple make any claims about this :)
     
  21. maflynn Moderator

    maflynn

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    #21
    My point is that the SSD space is limited the recovery partition shrinks the availability further. That means there's less SSD capacity to hold data.

    I'm saying that the Fusion drive cannot be faster then a pure SSD because it cannot hold of the data, and in fact the logic behind it moves data blocks based on usage. So there could be some things on the spinning drive and some on the SSD.
     

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