Slow SSD 750 EVO

Discussion in 'iMac' started by jseq, Nov 8, 2016.

Tags:
  1. jseq macrumors newbie

    Joined:
    Oct 17, 2010
    Location:
    Portugal
    #1
    Hi there, upgraded my 2012 27" iMac with an external ssd Samsung EVO 500Gb and Inateck FE2006 enclosure.
    All seems fine but when i run the Black Magic speed test i get random results on write, the first one is over 400 MB/s and after that it goes as low as 50 MB/s. The reading speed is consistently near 400 MB/s.
    Any thoughts?

    Thank you
     
  2. IngerMan macrumors 6502a

    IngerMan

    Joined:
    Feb 21, 2011
    Location:
    Michigan
    #2
    I would say for the lack of Trim support on USB3.0. If the Samsung does not have garbage collection then that will hurt. In order for garbage collection to work the drive needs left on. How much activity do you use your external SSD for, how full is it?

    You can google USB3.0 garbage collection and find some articles talking about this and bench marking.
     
  3. jseq thread starter macrumors newbie

    Joined:
    Oct 17, 2010
    Location:
    Portugal
    #3
    Well i´m running the OS from it and has 125Gb free, strange thing thou after a while the write speed goes back to 400 MB/s and then slows down again.
    I will check the USB3.0 garbage collection. Thanks
     
  4. IngerMan macrumors 6502a

    IngerMan

    Joined:
    Feb 21, 2011
    Location:
    Michigan
    #4

    I read that samsung Evo does have garbage collection. I recently installed a 275GB Crucial SSD MX300 also with garbage collection. If I leave the speed test on for over 8 cycles say at 5GB stress, it will drop down as well. If I go back to it a few minutes later it is back up to speed. I think that is just the reality of running an external SSD on USB. It may not effect the normal usage you are running with smaller writes and less frequent, unless you are using it for video encoding. Just my thoughts.
     
  5. Fishrrman macrumors G4

    Fishrrman

    Joined:
    Feb 20, 2009
    #5
    Inger wrote:
    "I would say for the lack of Trim support on USB3.0"

    This has absolutely nothing to do with it.
    Repeat, NOTHING.

    To the OP:
    Try a different enclosure.
    Or try a different ... drive.

    Your read speeds are close to where they should be.
    The "max" for using a USB3 enclosure and SSD is around 435mbps.

    I'm thinking that your slow write speeds are due to:
    - conflict between drive and enclosure
    - conflict between enclosure and Mac
    - possibly "a mix" of the above.

    Here's a test I did one minute ago, using a Sandisk "SSD Plus" 240gb drive hooked up to my late 2012 Mini via a USB3/SATA "adapter dongle":
    write: 347mbps
    read: 432mbps
    (Tested with BlackMagic speed test)

    Again, TRIM has NOTHING to do with the results you're getting.
    It's either the drive or the enclosure.
    I'd try a DIFFERENT ENCLOSURE as the first step.
    If you do, please save this thread and get back to us with your results.

    Final thought:
    I don't know why folks here consistently gravitate towards Samsung SSDs.
    I've seen numerous postings in this forum from folks having trouble with Samsung drives.
    I use other makers, such as Crucial and Sandisk, and NEVER have problems with them.
     
  6. bent christian Suspended

    bent christian

    Joined:
    Nov 5, 2015
    #6
    I am coming out of the same situation, except I use the Pro 850 and the Inatek FEU3NS-1E enclosure. I had terrible write speeds for a very long time (80MB/Sec to 200MB/Sec) with consistently good read speeds (430MB/Sec). It was very confusing. I tried just about everything, even going as far a reformatting the drive to start over. What I realize now, is that "starting over" really means zeroing out the drive. That go me back to 400MB/Sec write, 430MB/Sec read speeds. Then I did some reading on garbage collection. Idle time seems to be important, particularly if you write heavily to the drive and delete files. It is impossible to know when garbage collection is actually working, so I think we just need to let these machines sit for a time. Samsung SSDs use an active form of GC, which is supposed to work on the fly. It may not be able to keep up you do a lot of writing or if you delete files. If the enclosure has an LED, you can probably see the drive working after the system goes idle or you logout. This is appears to be garbage collection at work moving files around. Let the drive sit overnight with all accounts logged out. Unallocated space in the range of 20%-30% seems to be important as well. Re-partition the drive with 20%-30%, then delete the empty, untiled partition. This gives the drive new cells to write to and to move data around as it defragments. When the drive has to do this on the fly, it seems to result in decreased performance. If write speeds are not coming back for you, try zeroing out the drive in Disk Utility. Use the twice-over secure erase option. A simple reformatting is not what you want.
    --- Post Merged, Nov 8, 2016 ---
    I disagree. In my experience, TRIM is important to maintain consistent speeds in an SSD. BUT, we can get around this by allowing time for garbage collection to work. TRIM an GC work hand-in-hand to level wear and to ensure good cells are free. TRIM alerts GC as to where the files are they can be overwritten. GC will do this on it's own, but it takes more time to do so. TRIM/no TRIM, the end result will be the same, GC just takes more time getting there. If the users working habits are to shut the machine off after they are through working (as was mine), I think the drive never has time to defrag. Lately, I have been more lax and give the machine more idle time. Read write speeds are now back to where they were when the drive was new. Also, free, unallocated space seems to help keep the drive fresh.
    --- Post Merged, Nov 8, 2016 ---
    They are good drives. For example, I am getting about 53MB/Sec faster write speed on my 850 Pro. GC just seems a little wonky on these drives. I think I have it figured out.
     
  7. Fishrrman macrumors G4

    Fishrrman

    Joined:
    Feb 20, 2009
    #7
    I repeat:
    TRIM has NOTHING to do with it.

    I've been booting and running my 2012 Mini from USB3 since the day I unboxed it.

    The drives I've used run as fast after a year or two of use as they did when I first set them up.

    TRIM has made NO DIFFERENCE in performance AT ALL. EVER.
    I've never used it.
    (all shouting intentional).

    TRIM is one of the most-argued-over drive technology concepts of recent times.
    But it is "much ado… about nothing."
     
  8. bent christian Suspended

    bent christian

    Joined:
    Nov 5, 2015
    #8
    How do you know that TRIM is not an issue if you haven't ever used it? The OP is not using either of the drives you mentioned, so your experience is irrelevant. I use the 850 EVO in a Windows machine that supports TRIM and have never has a slow down. This is the exact same drive the OP is writing about. I have had speed issues on my 850 Pro. Yes, the issue here is most likely related to not having TRIM, as garbage collection is a proprietary function that varies from drive brand to drive brand. Your experience with Crucial and SanDisk garbage collection is useful as anecdotal, but largely irrelevant to the issue at hand.
     
  9. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #9
    I agree with you that TRIM is not the problem for OP here. If his drive was slow because of no TRIM, every write test would be slow, not just the second test.

    But I do disagree with your general comment that TRIM is "much ado… about nothing." You are just flat wrong about that and it has been demonstrated in the forums repeatedly.

    I get that you have had good luck without TRIM, but not everybody has been so lucky. There is post after post in here from people who were running their SSD without TRIM and the write speeds drastically slowed. Then by enabling TRIM and booting to single user mode and running "fsck -fy" in Terminal to TRIM unused blocks, full write speeds were restored.

    So just because you have had good luck without TRIM does not make it a non-issue.
     
  10. bent christian Suspended

    bent christian

    Joined:
    Nov 5, 2015
    #10
    That's not how SSDs work. SSDs use wear leveling across a drive. Also, active garbage collection in Samsung drives works on the fly. Other manufacturers, like Crucial use background GC, which works when the drive is idle. I don't know what SanDisk uses. Most likely, the drive is trying to deal with wear leveling and the deleted 1GB or 5GB dummy file that was just written by the speeds test, as the user is running another speeds test. Or it's writing to a new area of the drive (when speeds are good). I have done quite a bit of research on this drive and others like it (850 Evo/850 Pro). My research tells me these issues in Samsung drives appears to be related to GC and a lack of TRIM.
     
  11. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #11
    Yeah... could be. Unless this is causing a usability issue of some sort, I think it can be ignored regardless.
     
  12. bent christian Suspended

    bent christian

    Joined:
    Nov 5, 2015
    #12
    I had the exact same experience as the OP. I zeroed out the 850 Pro drive (not simply formatted), and the drive was back to 400/430 as it was new. That tells me the issue is related to a lack of TRIM, absolutely.
     
  13. Fishrrman macrumors G4

    Fishrrman

    Joined:
    Feb 20, 2009
    #13
    bent christian wrote:
    "I had the exact same experience as the OP. I zeroed out the 850 Pro drive (not simply formatted), and the drive was back to 400/430 as it was new. That tells me the issue is related to a lack of TRIM, absolutely."

    I've never used a Samsung SSD -- only Intel, Crucial, and Sandisk.
    Perhaps that's why I never saw a slowdown.

    There might indeed be some kind of "controller-based" garbage collection problem that is specific to Samsung (and perhaps with other drives that use a similar controller).

    But again, using non-Samsung drives (as mentioned above), I've never seen a problem. I do leave the computer "at idle" for periods of time, so perhaps the Crucial SSD is doing its garbage-collection then.

    I also occasionally use Drive Genius to zero-out the free space on my boot SSD's. Unsure if this makes a difference or not.

    Final note:
    I use an Intel SSD in my old MacBook Pro. I just checked System Profiler and it says that TRIM isn't enabled for it, either.
    No matter. From time to time, I boot it to another boot partition, and then run Disk Utility's "repair disk" function at it. I note during the repair process that DU puts up the message, "trimming unused blocks".
    That's good enough for me. The old MacBook still runs fine...
     
  14. bent christian, Nov 8, 2016
    Last edited: Nov 8, 2016

    bent christian Suspended

    bent christian

    Joined:
    Nov 5, 2015
    #14
    So you zero out free space on the drive, let it idle for GC, and TRIM through Disk Utility.

    Still willing to assert the OP issue has nothing to do with TRIM?
     
  15. campyguy macrumors 68040

    Joined:
    Mar 21, 2014
    Location:
    Portland / Seattle
    #15
    Owner of many Samsung SSDs chiming in here, most of them are in 2012 Mini Servers in either normal or RAID 0 setups, with a few in Win 10 PCs. I've had issues on occasion with 830, 840, and now 850 Pro SSDs as OS drives - and this slow down issue gets solved only by a secure erase, preferably two runs by a disk utility - we use DiskWarrior but Disk Utility will work just fine. This "slow down" issue isn't confined to OS X - we see it on our Win and Linux boxes too, and it's not a new issue or confined to a controller issue.

    My take it's either fixed by a secure erase or it's a bad disk - I now make sure that all of our Samsung SSDs are wiped via a dual secure erase when the box is opened... We enable TRIM but IMHO I've never noticed a difference...
     

Share This Page