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perthmacuser Level 1 Level 1

The new OWC Mercury Accelsior PCIe SSD specifies a PCIe 2.0 x 2 interface.  Does the x 2 mean what I think it does ... that it takes up two PCIe slots?


If so, this means that my Mac Pro 3.1 requires that I use at least one PCIe 1 slot (given I have an 8800GT in slot 1) and thus limit the potential of this SSD, right?  Or do I misunderstand this?

  • The hatter Level 9 Level 9

    PCIe 2.0 because 1.1/1.0 means it won't have bandwidth to run a full I/O.


    No it is not double width.


    In some cases people buy two to get the maximum thruput they are advertising.

  • perthmacuser Level 1 Level 1

    Thanks Hatter, I get the bandwidth difference (well, enough to understand that 2.0 allows more than 1.1/1.0) but I am confused about the 2.0 x 2.


    I am wondering if I can install this SSD into my 2nd PCIe slot (2.0 16 band) and get its full benefit.  I asked OWC via their blog but only learnt that "the interface is PCIe 2.0 x 2"


    Just a value for money question really ... if I get this SSD I will get a performance kick over my current 7200rpm boot and applications drive, just pondering how much.

  • The hatter Level 9 Level 9

    Macperformanceguide right now is the only one with published benchmarks on it so check there...

  • joevt Level 1 Level 1


    The Accelsior is a PCIe 2.0 x2 card. The x2 means that the link width can go up to 2 lanes. Physically, the card can fit into any PCI Express slot that can accept an x2 card. Electrically, the card has 2 PCIe 2.0 lanes. Each PCIe 2.0 lane can do 500 MB/s so 2 lanes can do 1000 MB/s which is enough to handle the 2 6Gb/s SATA III SSD's in the Accelsior (700 MB/s).


    All PCIe slots in all Mac Pros can physically accept x16 cards. Electrically, the slots are either x1, x4, x8, or x16.


    The Mac Pro 2008 has 2 PCIe 2.0 x16 slots (slot 1 and 2). The Accelsior will perform at it's full speed in those slots (PCIe 2.0 x2).


    Slots 1 and 2 of the Mac Pro 2006 and 2007 are PCIe 1.0 slots. Each lane in a PCIe 1.0 slot can do 250 MB/s. If you configure the slots to be x8 or x16 using the Expansion Slot Utility, then the Accelsior will do 380 MB/s in those slots (PCIe 1.0 x2).


    Slots 3 and 4 of the Mac Pro 2006, 2007, and 2008 are PCIe 1.0 slots. However, when you put an x2 card in slot 3 or 4, only 1 lane will be used because the ESB2 south bridge chip that controls those slots will not negotiate 2 lanes.  According to the PCI Express specifications, slots are not required to negotiate a link width of 2 lanes. The Accelsior in slots 3 and 4 only does 195 MB/s (PCIe 1.0 x1).

  • perthmacuser Level 1 Level 1

    So, if I read you correctly, I can install an Accelsior into my second slot (leaving graphics card in slot 1) and get full speed from the SSD? 

  • joevt Level 1 Level 1

    Correct. The card only takes one slot. A PCIe 2.0 slot (such as slot 2 in the Mac Pro 2008) will give you full performance from the Mercury Accelsior.


    Check About This Mac... -> More Info... -> System Report... -> PCI Cards -> pci1b4b,9230. You should see something like this:




      Type: AHCI Controller

      Driver Installed: Yes

      MSI: Yes

      Bus: PCI

      Slot: Slot-2

      Vendor ID: 0x1b4b

      Device ID: 0x9230

      Subsystem Vendor ID: 0x1b4b

      Subsystem ID: 0x9230

      Revision ID: 0x0010

      Link Width: x2

      Link Speed: 5.0 GT/s


    If you see Link Speed: 2.5 GT/s then it means you put the card in a PCIe 1.0 slot.


    If you see Link Width: x1 then it means the slot was not able to negotiate 2 lanes to the Accelsior card.

    There are a few minor booting issues I've found with the Accelsior in a Mac Pro 2008 (minor if you don't care about Boot Camp):


    If I hold option key down during startup to see the Startup Manager, then the Startup Manager will not show the partitions on the Accelsior. This means I can't use Recovery HD from the Accelsior. I need to keep an OS on a normal hard drive for emergencies.


    I am unable to boot Windows or Linux (using Boot Camp) from a CD/DVD, from a hard drive, or from the Accelsior, while the Accelsior is installed. This means I can only use virtualization software (such as Parallels Desktop) to run Windows.


    If I boot rEFIt or rEFInd from the Accelsior, then they will not show partitions from other hard drives. If I boot rEFIt or rEFInd from a hard drive, they will not show partitions on the Accelsior.

  • perthmacuser Level 1 Level 1

    Good to know I can get full Accelsior speed.  Pity about the Boot Camp issues.  I have Windows installed on a separate HDD which is occasionally accessed via Boot Camp.  So I will need to remove the Accelsior to boot windows?

  • joevt Level 1 Level 1

    That has been my experience on the Mac Pro 2008. I have been unable to use my Boot Camp partitions no matter where they are located unless I remove the Accelsior.


    I haven't found any other users that have noted success or failure with Boot Camp on the old Mac Pros (2006, 2007, 2008) with the Accelsior card installed.


    I can still use Parallels Desktop for Mac to boot my Boot Camp partitions while running Mac OS X though.

  • GreatScottie Level 1 Level 1

    I received 2 of these cards the day OWC made them available.

    FWIW my benchmarking was in the ballpark of the published MPG numbers but not identical.

    I have them both installed on a 2010 MacPro. They worked fine on SL & now on Lion.


    Downside: I cold not get Lion to install on a RAID-0 config of both drives. The install barfed.

    Instead, I partitioned both cards to give me ~80GB boot partition on 1 card, another ~80GB partition on the other card and then I created a stripe-0 volume across the other ~40GB partitions on each card giving me 3  ~80GB partitions.


    Here's the numbers for both the ~80GB scratch disk & the ~80GB RAID-0 partition:-





    Using test size of 2GB, 4MB at a time at start (0%), within a 72.0GB test file.


    Iteration 1: writing…673MB/sec, reading…685MB/sec

    Iteration 2: writing…662MB/sec, reading…686MB/sec

    Iteration 3: writing…670MB/sec, reading…684MB/sec

    Iteration 4: writing…671MB/sec, reading…688MB/sec

    Iteration 5: writing…670MB/sec, reading…688MB/sec



      Monday, May 28, 2012 3:12:33 PM Pacific Daylight Time, volume "Accelsior-Single" (74.4GB) 


    ------------ Averages for "Accelsior-Single" (2GB/4MB, 5 iterations) -----------

    Iteration           Write MB/sec          Read MB/sec

         1                    673                  685   

         2                    662                  686   

         3                    670                  684   

         4                    671                  688   

         5                    670                  688   


      Slowest                 662                  684   

      Fastest                 673                  688   

      Average                 669                  686   

       Median                 670                  686   

       Range                 11.7                  4.49  


    Command "run-sequential" executed in 31.00 seconds on Monday, May 28, 2012 3:13:04 PM Pacific Daylight Time



    Using test size of 2GB, 4MB at a time at start (0%), within a 71.2GB test file.


    Iteration 1: writing…1234MB/sec, reading…1269MB/sec

    Iteration 2: writing…1184MB/sec, reading…1265MB/sec

    Iteration 3: writing…1182MB/sec, reading…1288MB/sec

    Iteration 4: writing…1172MB/sec, reading…1267MB/sec

    Iteration 5: writing…1171MB/sec, reading…1276MB/sec



      Monday, May 28, 2012 3:13:18 PM Pacific Daylight Time, volume "Accelsior-RAID" (73.6GB) 


    ------------- Averages for "Accelsior-RAID" (2GB/4MB, 5 iterations) ------------

    Iteration           Write MB/sec          Read MB/sec

         1                   1234                  1269  

         2                   1184                  1265  

         3                   1182                  1288  

         4                   1172                  1267  

         5                   1171                  1276  


      Slowest                1171                  1265  

      Fastest                1234                  1288  

      Average                1189                  1273  

       Median                1182                  1269  

       Range                 63.6                  22.1  


    Command "run-sequential" executed in 17.10 seconds on Monday, May 28, 2012 3:13:35 PM Pacific Daylight Time





    You can see that RAIDing these cards boosts your "full-performance" very nicely... almost twice as fast.


    One other thing, contrary to other posts, I am able to boot from a separate SSD into Windows just fine... except it takes 7.5 minutes to boot. Once booted Windows runs fine. Boot time for OS X also increases when the Accelsior cards are installed (just like other PCIe SSD cards).


    I expect a third Accelsior would boost "full-performance" higher... MPG posted a few details on there findings, but not until after I tested it for myself by RAIDing 2 Accelsiors with an OCZ Revo Drive (also a PCIe card).

    My results again were in the ball park that MPG posted, but I did get better visibility as to performance ranges that MPG did not publish by using benchmarks available through Windows.


    So to answer someone els's Q, no you should not have to physically remove your Accelsior cards in order to boot into Windows from a separate drive.

  • The hatter Level 9 Level 9

    did your mix of two different cards affect your tests?

    creaating an array to boot from?

    perhaps try with just the two Accelsiors?

  • GreatScottie Level 1 Level 1

    Not sure what you mean.


    > did your mix of two different cards affect your tests?


    I was providing info rather than asking Q's.


    The test results I quoted were only from:


    (1) a single Accelsior partition on a single card

    (2) a single Accelsior RAID-0 volume striped from 2 identical Accelsior cards.


    I think the test results are within the same ballpark as MPG (actually maybe a bit better than their published results).


    > creaating an array to boot from?


    Given the far superior results when putting 2 Accelsiors into a RAID-0 config then why wouldn't I try this given OWC claims the cards are bootable. Actually, the Lion installation thought it could do this since it gave a warning that since my boot drive was a RAID config some features wouldnt be available, such as filevault... the installer was still quite happy to waster over an hour with me "doing the installation" to my Accelsior RAID boot drive, before it decided to declare it failed.


    > perhaps try with just the two Accelsiors?


    Try the installation with just the 2 Accelsiors? Thats what did not work, but I got past that limitation.

    Like I said I got Lion installed using partition #1 of Accelsior #1.

    I created a SingleAccelsior partition #1 on Accelsior #2.

    I created a RAID-0 volume combining both partitions #2 from Accelsior #1 & #2.

    This all worked and what the performance results I showed represent.


    Not sure what it is that I should try ... the Windows partition that does install is on a separate SSD.

    I mentioned this since I read in this thread claims that Windows couldnt boot if the Accelsiors were installed & I was informing those posters that it is possible.

  • joevt Level 1 Level 1

    There are various ways to get Lion on a software RAID. It just takes a little extra work.



    When you create a raid set, Disk Utility automatically adds an Apple_Boot partition called "Boot OS X" to each hard disk. The "Boot OS X" partition is used to boot OS X when it's installed on a raid set. The only thing left for you to do is to get OS X onto the raid set. The Lion installer sometimes fails at that because of the Recovery HD. I think the simplest method may be to use Disk Utility's Recover option to copy your existing Lion partition to the raid set. If you use Recover from Disk Utility to copy a Lion partition, it will also try to copy the associated Recovery HD partition as well if it exists. This won't work when the destination partition is a raid set. The workaround is to use Carbon Copy Cloner instead, or temporarily change the partition type of the Recovery HD partition from Apple_Boot to Apple_HFS using iPartition, gpt fdisk (gdisk or cgdisk ), or gpt. Once the Restore is complete, you can revert the partition type of the Recovery HD back to Apple_Boot.



    The problems I'm having with Boot Camp and the Accelsior probably have to do with the older EFI firmware of the Mac Pro 2008. Apple doesn't make firmware updates for older Macs. I'm waiting for someone with a 2006, 2007, or 2008 Mac Pro to chime in on Boot Camp issues.

  • nycaleksey Level 1 Level 1

    Has anyone found any solution to running BootCamp with this PCIE SSD?

  • joevt Level 1 Level 1

    I haven't found a solution for running Boot Camp while the Accelsior is installed in my Mac Pro 2008. I also haven't found any other complaints about Boot Camp with the Accelsior SSD either. Actually one person with a Mac Pro 2009 with an Accelsior says it took 15 minutes for Windows to appear but the description of the problem was missing some details. Windows does not appear if I wait 15 minutes or an hour. Another Mac Pro 2009 user has no problem booting Windows from a SATA drive when an Accelsior is installed.


    OWC has not explicetly confirmed or denied this Boot Camp incompatibility with the old Mac Pros on any website but they did add my user rating/review that mentions the problem to their Accelsior 480 GB page.


    Have you purchased the card? What kind of Mac do you have? Are you experiencing issues?


    I'm thinking the solution might involve rewriting some Compatibility Support Module (CSM) stuff in EFI so that it ***** less on the old Mac Pros. sible-firmware-interface/efi-compatibility-support-module-specification-v097.htm l

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