High amount of writes even when idling

Discussion in 'OS X Mavericks (10.9)' started by yjchua95, May 7, 2014.

  1. yjchua95 macrumors 604

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    #1
    G'day y'all,

    On my 21.5" late-2013 iMac, Activity Monitor shows about 300MB written to the internal SM0256F SSD every 5 minutes or so. In the space of half an hour when idling, almost 2GB of data is written to it.

    I'm worried about this because I've heard that SSDs have a finite amount of writes that it can handle.

    This problem doesn't occur on my 27" iMac and both my rMBPs.

    On a side note, no external hard drives are connected to the iMac as well.
     
  2. h9826790 macrumors 604

    h9826790

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    #2
    Don't worry about the SSD write cycle, most likely you will change few computers before it die.
     
  3. yjchua95 thread starter macrumors 604

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    #3
    Normally how many write cycles can a MLC-based SSD withstand? At the rate it's going, it seems to be writing 40GB daily when idling.

    I may have to consider a clean install of Mavericks soon to fix this problem. Repairing disk permissions didn't help.
     
  4. Hellhammer Moderator

    Hellhammer

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    #4
    Samsung rates the 840 Pro (their only MLC drive for clients) at 40GB per day for 5 years. That's 73TB of writes in total.
     
  5. yjchua95 thread starter macrumors 604

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    #5
    Update:

    3 hours from boot, my iMac has written 25.07GB of data when idling. Reads in and reads out values are 7,487,469 and 1,363,778 respectively.

    6 hours and 10 minutes from boot, my 15" rMBP has only written 3.13GB of data when idling. Reads in and reads out values are 187,012 and 110,416 respectively.
     

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  6. yjchua95 thread starter macrumors 604

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    #6
    Thanks.

    I have a 512GB 840 Pro in my 2011 MBP, but on that machine, it doesn't write so much when idling compared to my iMac.
     
  7. h9826790 macrumors 604

    h9826790

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    #7
    I think that's just for their warranty, not the life span of the SSD.

    "For enterprise applications, 5 years limited warranty assumes a maximum average workload of 40GB/day (calculated based on host writes and on the industry standard of 3-month data retention). Workloads in excess of 40GB/day are not covered under warranty."

    Samsung_SSD_840_PRO_Brochure_2.pdf

    I couldn't find the life span estimate from the Samsung webpage. However, from the following link. It indicate that the 840 pro MLC SSD can stand for about 10 years with 40G/day.

    http://www.anandtech.com/show/6459/samsung-ssd-840-testing-the-endurance-of-tlc-nand
     
  8. w00t951 macrumors 68000

    w00t951

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    #8
    The argument that it's not important because it's covered by the warranty isn't very smart.

    There's a problem - OS X is mysteriously writing large amounts of data to the disk. I'd want to stop it regardless of the SSD's durability (which, by the way, isn't something that's well understood).

    In addition to the SSD damage and extra garbage collection necessary, file operations can lead to file system failure. HFS+ is a very fragile and outdated file system writing many files can increase the probability of (catastrophic) failure.

    Also, it's unnerving having unknown data written to the disk. Small amounts are caches and normal running processes, but huge amounts like that are concerning.

    Have you checked your swap outs? Go to Activity Monitor > Memory and check it out.
     
  9. yjchua95 thread starter macrumors 604

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    #9
    Swap used is 0 (it's got 16GB of RAM, so I'd be astonished if it was using swap when idling).

    I found out the culprit last night, it was due to the idle-time scan feature in Norton Internet Security (as much as I detest Norton's products, my employer forced me to install it on my computers that were used for work).

    After disabling idle-time scan, the high amount of writes vanished.
     
  10. w00t951 macrumors 68000

    w00t951

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    #10
    Nice. I've got 16GB of RAM myself, but even when memory pressure is low there is consistently 200-300MB of swap used.
     
  11. h9826790 macrumors 604

    h9826790

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    #11
    Shouldn't be like this, when my Mac Pro only have 16G of RAM. Even though my machine run 24/7, the OS almost never use any swap.

    For 10.9.2, the OS itself will continuously use about 6.5G of RAM, for a 16G system, should be no need to touch the swap file when no memory pressure.
     
  12. w00t951 macrumors 68000

    w00t951

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    #12
    Right? But I'm always seeing 200-300MB of swap used. Doesn't make sense.
     
  13. h9826790, May 10, 2014
    Last edited: May 10, 2014

    h9826790 macrumors 604

    h9826790

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    #13
    I will say that is abnormal.

    For your info. This is the RAM usage on my machine in the last 7 days. The swap file size always stay at zero.
     

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  14. yjchua95 thread starter macrumors 604

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    #14
    To me it's normal. Mavericks will always use as much RAM as possible. In Mavericks, free RAM is wasted RAM.

    As long as your memory pressure stays green and swap doesn't reach too high, your system is fine.

    On my 27" iMac (32GB RAM), I've seen RAM usage spike all the way past the 20GB mark even when idling (but it happened only after I closed RAM-intensive apps), although app memory was only around 5GB.
     
  15. h9826790, May 10, 2014
    Last edited: May 10, 2014

    h9826790 macrumors 604

    h9826790

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    #15
    I know my machine is normal. I mean w00t951's machine swap file should stay at zero size when the memory pressure is low.

    I was with 32G RAM, but I just realise my machine run faster with only 3x8G RAM. I don't know how about iMac, but for my triple channel Mac Pro, I better only use 24G. Anyway, my machine also stay at around 22G RAM usage even though I have 32G.
     
  16. yjchua95 thread starter macrumors 604

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    #16
    Ohh sorry, I thought you meant your graphs were abnormal :p
     
  17. h9826790 macrumors 604

    h9826790

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    #17
    Sorry for my poor English :D
     
  18. yjchua95 thread starter macrumors 604

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    #18
    It's all right, your English is better than most :)

    I've come across some people who live in an English-speaking country, but their English is really atrocious :)
     

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