11 Replies Latest reply: Jul 21, 2011 1:27 AM by Brett Pearce
barubin Level 1 Level 1 (15 points)

I am familiar with OS's that use virtual memory (VM) since the late 1980's and the rule of thumb has been to be prepared to have enough HDD space equal to 100% of RAM installed. 20% of a multi TB HDD seems an excessive amount of space devoted to VM. Is there a technical reason for this or is this something to ignore.

 

TIA.


24, Mac OS X (10.6.7)
  • Sjazbec Level 4 Level 4 (1,670 points)

    1) Time Machine now stores shadow copies on the internal Disk so you can browse backups even if the external disk or time capsule is not available.

     

    2) Version Control feature : Lion takes snapshots ( in supported apps like preview,textedit,iwork 9.1 .. ) of each edited document, thus storing more then only one copy of any file which you can browse and restore to any wanted version later.

     

    3) Lion creates a hidden recovery partition to desaster-restore the complete OS if it fails to start ( thus making DVD obsolete )

     

    those fancy and cool features surely need space, hidden from the user and only visible "on demand" - so a permanent virtual safe storage container inside the physical disks visible file system makes sense.

  • barubin Level 1 Level 1 (15 points)

    Sjazbec,

     

    Thanks for the quick response. Now for the new questions:

     

    My iMac I plan to put Lion on has an upgraded internal HDD of only 500 GB. Since my family depends upon this computer for EVERYTHING, I plan to move all home directories to an 800 FW external HDD, image the remaining files to another, bootable, 800 FW externao HDD, test everything, and then repartition the 500 GB for 10.6.8 and Lion (I think I'll create a Boot Camp partition for Windoze 7 instead of using Fusion). I'm using an 800 FW external HDD for Time Machine now. Is there anything that will not work with the new way Time Machine functions?

     

    With the Version Control feature, are the versions stored in the home directories or the owners/creators, I hope, or elsewhere?

     

    Is the hidden recovery partition a full Lion OS or just an install/reinstall package? In either case, would I be able to Option-boot select it and use it to run the Disk Utility repair function on the other partitions?

     

    TIA.

     

    --Bruce

  • barubin Level 1 Level 1 (15 points)

    Sjazbec,

     

    I found the answer to my last question:

    Is the hidden recovery partition a full Lion OS or just an install/reinstall package? In either case, would I be able to Option-boot select it and use it to run the Disk Utility repair function on the other partitions?

    http://web.me.com/pondini/AppleTips/RecoveryHD.html

     

    Macs with Lion have a hidden partition on their internal HDs containing a "Recovery HD."

                   

    This is the rough equivalent of having a copy of an OSX Install Disc on your system, but is much more convenient (except for the Reinstall OSX option, which is much slower).   

     

    You may also be able to create a Lion Install disc or partition after purchasing Lion from the AppStore (but not after Reinstalling via the Recovery HD).  See Making a Lion Install disc or partition for instructions.

     

    There are a number of options once booted into the "Recovery HD" as part of the "Mac OS X Utilities".

     

    • Firmware Password Utility
    • Network Utility
    • Terminal
    • Restore From Time Machine Backup
    • Reinstall Mac OS X  (Set up and install a new copy of Lion)
    • Get Help Online
    • Disk Utility

     

    Thanks Apple!

     

    --Bruce


     


  • etresoft Level 7 Level 7 (26,880 points)

    barubin wrote:

     

    Why does Lion "perform best with at least 20% of your hard drive free"?

    Where did you get that information?

     

    If you are on a notebook, Lion may periodically clean up temporary files once your free disk space drops below a certain threshold. That threshold is set dynamically and can be different for every machine. On my 2007 Macbook with a 250 GB hard drive, I do indeed have a 20% threshold where Lion starts to clean up my local backups and other files. On a different computer, it could be more and it could be less. I only know about my own machine. I don't know how it would work on a desktop with a multi -TB drive.

  • Graham Perrin Level 2 Level 2 (255 points)

    Sjazbec wrote:

    3) Lion creates a hidden recovery partition to desaster-restore the complete OS if it fails to start ( thus making DVD obsolete )

     

    The hidden Apple_Boot Recovery HD partition typically occupies 650.0 MB on disk (reported by diskutil) and should be ignored when thinking of free space on the normal startup volume.

  • barubin Level 1 Level 1 (15 points)

    etresoft,

     

    MacOutfiters sent me an email this morning at they wrote:

     

    For best performance:
    For the very best performance with Lion,
    MacOutfitters recommends a minimum of 4GB of RAM installed.
    Also, your Mac will perform best with at least 20% of your hard drive free.

  • Rob Palmer4 Level 2 Level 2 (185 points)

    Barubin,

     

    The reason for that is to allow the operating system to swap data in and out of RAM. The industry standard for file servers is 80% maximisation, so the fact that lion can cope with that is actually quite good. Be glad that you're not running something like MS SQL, the industry standard for that is 60% maximum utilisation - and that even applies to multi terra byte systems.

  • barubin Level 1 Level 1 (15 points)

    Rob Palmer4,

     

    As I stated when I started this thread, the rule of thumb for virtual memory (VM) was to have enough space equal to the installed RAM. So if 100% of 4GB of RAM is swapped out to a 2TB HDD, then 4GB of space on the 2TB would be required, not 400GB (20% of 2TB).

     

    I found Sjazbec's response reasonable along with Graham Perrin's more detailed answer (The hidden Apple_Boot Recovery HD partition typically occupies 650.0 MB on disk).

  • etresoft Level 7 Level 7 (26,880 points)

    I don't dispute that advice. I was just wondering if you had heard something authoritative from Apple. I haven't. I have heard that the cut off point varies depending on your system configuration. I can say that I definitely had a message in my Lion log files that said something equivalent to "less than 20 percent free disk space, cleaning up". I forget the exact wording, but on my machine, it is 20 %.

  • Rob Palmer4 Level 2 Level 2 (185 points)

    I can't say if it's the case for Lion, but certainly for database servers, the reason that you only want to use 60% of the hard drive space (with traditional disks, not sure about ssd's) is as using more than this results in the disk head having to move further to read the data - resulting in slower IO times.

     

    As a result, in order to maximise the IO throughput you want to minimise the fragmentation of files on the disk and stay away from the longer tracks on the outside of the disk which drastically reduce the disk IO.

     

    So assuming that this affects lion (which is fair enough as it affects all traditional disks), you'll notice a drop off in the disk speed, and so a reduced user experience, from a nearly full disk.

     

    Hope that makes sense, as I say I'm not sure if this is the case for lion - but I'd be shocked if it didn't suffer from this as all physical disk systems do. All that changes is the percentage that it becomes obvious and that is dependent on how the disks are used and not the os that's being run.

  • Brett Pearce Level 1 Level 1 (20 points)

    barubin wrote:

     

    Sjazbec,

     

    Thanks for the quick response. Now for the new questions:

     

    My iMac I plan to put Lion on has an upgraded internal HDD of only 500 GB. Since my family depends upon this computer for EVERYTHING, I plan to move all home directories to an 800 FW external HDD, image the remaining files to another, bootable, 800 FW externao HDD, test everything, and then repartition the 500 GB for 10.6.8 and Lion (I think I'll create a Boot Camp partition for Windoze 7 instead of using Fusion). I'm using an 800 FW external HDD for Time Machine now. Is there anything that will not work with the new way Time Machine functions?

    Found out the hard way that Boot Camp needs one Mac partition to work. I did what you plan (10.6 & 10.7 partitions) then tried to run Boot Camp - no go.