Why is my iMac writing data to the disk?

Discussion in 'iMac' started by PatriotInvasion, Nov 24, 2010.

  1. PatriotInvasion macrumors 68000


    Jul 18, 2010
    Boston, MA
    Ok, so everyone knows the iMac hard drive can be a little noisy, but I just want to know what exactly is being "written" to the disk while doing normal tasks like web surfing.

    I often use Safari and can hear the hard drive churning and Activity Monitor will show high red spikes of written data. What is this data being written? Is it normal?

    Here's a screen shot of my Activity Monitor while web surfing and watching video with my EyeTV device. Does this look like normal activity to you?

    Attached Files:

  2. smithrh macrumors 68020


    Feb 28, 2009
    Absolutely normal.

    The number of things that are written to and read from disk are enormous.

    In this case, eyetv is reading from disk (note, this is based on what you said, and not the activity monitor). I'm not sure if you're recording or watching (or both), but either one is going to be disk intensive.

    Safari also caches just about everything it can get it's hands on. This is normal for web browsers. If your going to cache something, well, you have to write it to disk.

    If you were to quit all apps and just let your Mac sit there for a bit, disk accesses (both read and write) should drop down to very low levels or even zero.
  3. PatriotInvasion thread starter macrumors 68000


    Jul 18, 2010
    Boston, MA
    Thanks for that response. In this scenario, I was only watching TV with EyeTV, although it is the EyeTV HD model so the video was in 1080i. Makes sense about Safari as well. I was just curious because of the churning noises coming from the hard drive without me downloading anything so I opened up Activity Monitor and saw the high red spikes. Sounds like this is the way it's supposed to be so I feel better now, thanks.:)

    And yes, if I shut down all Apps, after a minute or so the read/write activity goes way down.
  4. Mr. Savage macrumors regular

    Mr. Savage

    Jun 11, 2010
    Also check your eyetv live tv buffer in prefernces>recording. There's an option to keep your buffer in RAM which keeps from writing to disk.
  5. unixfool macrumors 6502a

    Jan 21, 2006
    Northern VA

    Good stuff...I agree the above, with the exception of the disk activity levels dropping to low or zero levels. "low levels" would have to be defined, but I doubt that any machine will ever have zero disk reads and writes.

    OS X is *nix. Even if a user quits all apps, there's still going to be lots of logging (which will either read or write, or even both) going on, unless the machine has 90+% of its services (daemons) disabled. Even then, there will be some things that will continue to log. It will also depend on what the admin/user has the system configured. For example, if your router is port-forwarding traffic to port 22 on your Mac, you're always going to see internet traffic trying to access the SSH service and those access attempts will be logged.

    I imagine something similar happens with MS operating systems.
  6. davids8477 macrumors 6502

    Jan 4, 2008
    Remember that EyeTV also records a buffer so that you can go back X minutes. I think this is adjustable.

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