tjeerdkramer

Q: Slow performance with Samsung 850 pro SSD in raid 0

I have just upgraded my mac mini (late 2012) with dual Samsung 850 Pro SSD's and put them in RAID 0 mode. The weird thing is, benchmarks show read speeds of 88 MB/sec ? This is way to slow, was expecting at least 500 MB/s and over!

 

Any idea on what I can do here?

Posted on Nov 12, 2015 1:16 AM

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Q: Slow performance with Samsung 850 pro SSD in raid 0

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  • by lllaass,

    lllaass lllaass Nov 12, 2015 1:27 AM in response to tjeerdkramer
    Level 10 (188,811 points)
    Desktops
    Nov 12, 2015 1:27 AM in response to tjeerdkramer

    In Profiler

    OS X: About System Information and System Profiler - Apple Support

    under SATA what negotiated link speed is listed?

     

    How are you measuring speed?

    The Black Magic app?

  • by tjeerdkramer,

    tjeerdkramer tjeerdkramer Nov 12, 2015 2:19 AM in response to lllaass
    Level 1 (0 points)
    Nov 12, 2015 2:19 AM in response to lllaass

    Yes I tested with the blackmagic tool, but also with several terminal commands such as


    tjeerdkramer@quarterpounder:~$ write=$(dd if=/dev/zero bs=2048k of=tstfile count=1024 2>&1 | grep sec | awk '{print $1 / 1024 / 1024 / $5, "MB/sec" }')

    tjeerdkramer@quarterpounder:~$ echo $write

    151.151 MB/sec

     

    151 is actually one of the best scores I have seen. Ranges between 60 and 150 MB/s

     

    Intel 7 Series Chipset:

     

      Vendor: Intel

      Product: 7 Series Chipset

      Link Speed: 6 Gigabit

      Negotiated Link Speed: 6 Gigabit

      Physical Interconnect: SATA

      Description: AHCI Version 1.30 Supported

     

    Samsung SSD 850 PRO 512GB:

     

      Capacity: 512,11 GB (512.110.190.592 bytes)

      Model: Samsung SSD 850 PRO 512GB             

      Revision: EXM02B6Q

      Serial Number: S250NXAG901360J   

      Native Command Queuing: Yes

      Queue Depth: 32

      Removable Media: No

      Detachable Drive: No

      BSD Name: disk0

      Medium Type: Solid State

      TRIM Support: No

      Bay Name: Lower

      Partition Map Type: GPT (GUID Partition Table)

      S.M.A.R.T. status: Verified

      Volumes:

    EFI:

      Capacity: 209,7 MB (209.715.200 bytes)

      BSD Name: disk0s1

      Content: EFI

      Volume UUID: 0E239BC6-F960-3107-89CF-1C97F78BB46B

    disk0s2:

      Capacity: 511,77 GB (511.766.216.704 bytes)

      BSD Name: disk0s2

      Content: Apple_RAID

    Boot OS X:

      Capacity: 134,2 MB (134.217.728 bytes)

      BSD Name: disk0s3

      Content: Apple_Boot

      Volume UUID: 71462A61-72B7-3BAC-91D0-93A34E417C0C

  • by lllaass,

    lllaass lllaass Nov 12, 2015 7:37 AM in response to tjeerdkramer
    Level 10 (188,811 points)
    Desktops
    Nov 12, 2015 7:37 AM in response to tjeerdkramer

    Do y have the latest firmware for the SSDs?

    Do you have TRIM enabled?

    I have heard of problems with the 850 Pro in Macs

    http://www.mac-help.com/threads/samsung-850-evo-ssd-performance-issues.220356/

  • by keg55,

    keg55 keg55 Nov 12, 2015 8:26 AM in response to lllaass
    Level 6 (8,407 points)
    Mac OS X
    Nov 12, 2015 8:26 AM in response to lllaass

    He doesn't have TRIM enabled (see his post above).

     

    TRIM Support: No

  • by John Lockwood,

    John Lockwood John Lockwood Nov 13, 2015 1:56 AM in response to tjeerdkramer
    Level 6 (9,309 points)
    Servers Enterprise
    Nov 13, 2015 1:56 AM in response to tjeerdkramer

    I am only seeing details in your post for a single drive which is a Samsung SSD 850. I am sure it is not the case but if the other drive was a slow spinning metal hard drive it would slow the entire RAID down.

     

    I don't recall it occurring on Mac minis but there have been cases of MacBook Pros fitted with two hard drives of one being incorrectly limited to SATAII instead of SATAIII, hence the need to check details of both.

  • by tjeerdkramer,

    tjeerdkramer tjeerdkramer Nov 13, 2015 2:02 AM in response to John Lockwood
    Level 1 (0 points)
    Nov 13, 2015 2:02 AM in response to John Lockwood

    Hope these screenshots help?1.gif2.gif3.gif4.gif

  • by John Lockwood,

    John Lockwood John Lockwood Nov 13, 2015 3:28 AM in response to tjeerdkramer
    Level 6 (9,309 points)
    Servers Enterprise
    Nov 13, 2015 3:28 AM in response to tjeerdkramer

    Thanks yes those confirm both drives are running at SATA III i.e. 6Gbps.

     

    It maybe you have them setup as RAID1 a mirror rather than RAID0 a stripped array. With RAID0 it should give you the equivalent of a 1TB drive by 'striping' the two 512GB drives together and reading/writing half from each simultaneously. As the RAID volume is only 511GB it looks like you have a RAID1 array whereby an exact duplicate copy is on both drives. This means that if a single drive fails you still have all your data but it also means it has to write a copy to both drives which of course takes twice as long. I would however not have expected it to cause a slow down in reads as it only needs to read one copy.

     

    Here is a very rough diagram to illustrate how RAID0 and RAID1 would differ.

           

              (-512GB-)
    Drive A = AAAAAAAA
    Drive B = BBBBBBBB
    
              (-512GB-)
    RAID1   = 11111111
              11111111  i.e. both drives have same content
    
              (-----1TB------)
    RAID0   = 1212121212121212  i.e. each drive has half the content
    
    

     

    There is also the issue that software based RAID like you are using is always slower than a hardware based RAID, and Apple's particular software RAID is also slower than for example SoftRAID5. See http://www.softraid.com

     

    Even so your read speeds are far slower than I would expect.

     

    If it is possible I would consider wiping it all and setting it up again from scratch.

  • by tjeerdkramer,

    tjeerdkramer tjeerdkramer Nov 13, 2015 4:07 AM in response to John Lockwood
    Level 1 (0 points)
    Nov 13, 2015 4:07 AM in response to John Lockwood

    I have removed the RAID altogether, erased the drives, and tested again. Still very poor performance (write 80-120 MB/S, read max 200 MB/s). Both drives seem to have the same kind of performance...

  • by lakorai2,

    lakorai2 lakorai2 Apr 18, 2016 8:10 AM in response to tjeerdkramer
    Level 1 (4 points)
    Apr 18, 2016 8:10 AM in response to tjeerdkramer

    Try the following:

     

    Run the trimforce command. Upgrade your Machine t o at least 10.10.5 or 10.11. Now run the following command from the Terminal:

     

    "sudo trimforce enable". Enter in your password.

     

    Hit enter. Read the scary Apple warning message and say Yes. Say yes to rebooting the machine.

     

    This will make a big difference.

     

    You are running a SATA 6/GB /sec capable Intel chipset, so you definitely should be hitting over 500 Megabytes per second.