What path a remotely Mac copied file follows ?

Discussion in 'Mac OS X Server, Xserve, and Networking' started by i-Moi, May 8, 2011.

  1. i-Moi macrumors newbie

    Feb 27, 2010
    Hello everyone,

    (Please forgive my english, I'm writing from France)

    I know nothing more about the networks that the basic Mac user, and I have a question, simple to state, but which answer may be more complicated.

    When a Mac copies a file between a network drive (NAS) and an external USB drive attached to this NAS, do the files pass through the Mac or does he manage the process 100% remotely?

    i.e, let's say I'm moving to a new house, and I need my stuff to be carried : friends came to help. I want Adam to give a box to Ben. I'm Mac. Do I have to take the box from Adam and give it to Ben, or can I just yell and tell them what I want, without having to break my back ? (I'll buy them dinner afterwards in a nice french restaurant, of course)

    In the first case, the resource requirements (bandwidth, 3 disks activity, CPU, RAM, etc.) are heavy, in the other case, it's more a background task.

    This question arises from a particular case, BTW:
    I want to make a regular backup of my NAS HDD (in this case, a Popcorn Hour NMT C200 which offers an SMB share) to a USB attached external drive, and I have no knowledge of any tool for that.

    So it looks like I'm reduced to a miserable choice:
    -either I do the backup manually, file by file, through the -pita- NMT PCH C200 user interface.
    -or do it from my Mac, in which case I do not know what would be the perfect tool for it : Carbon Copy Cloner ? Terminal ? (I'm looking for an automated incremental backup).

    Thank you all for your advice.

  2. mrbash, May 13, 2011
    Last edited: May 13, 2011

    mrbash macrumors 6502

    Aug 10, 2008
    In your situation, the file will will travel over the network to your network interface, up through the network stack, onto your Mac's memory. It will then travel from the RAM to the CPU, and into another portion of memory, and eventually back onto the CPU then the PCI bus, and onto your USB device.

    You can automate the back up by using a cron task, or you can purchase a backup software program that does what you want. SuperDuper is pretty good. I'm unsure what can perform incremental back-ups, but you can always use 'rsync' to reduce the amount of data you are transferring, but at the cost of more CPU utilization.

    'rsync' will calculate a delta and copy that delta into the same location on your backup instead of keeping the delta in a separate location like Time Machine.

    I use 'rsync' in a cronttab to keep my Lightroom files backed up to an off-site server.
  3. Transporteur macrumors 68030

    Nov 30, 2008
    No need to buy anything. Carbon Copy Cloner can be scheduled by design and actually uses rsync for the heavy lifting, so incremental backups are no problem. Basically it is just a nice GUI for rysnc, but does the job very nicely.
    I use it on a daily basis to make a clone from my boot drive, but use the standard rsync to backup data on my server, scheduled via iCal. :)

    At any rate, unless the sync process is triggered by the NAS itself, the data will always take a detour around the Mac.
  4. jtara, May 14, 2011
    Last edited: May 14, 2011

    jtara macrumors 68000

    Mar 23, 2009
    It's a bit of a tricky question! The answer is, it depends.

    The answer given above is correct, if you use Finder or a command-line copy on your Mac to initiate the transfer.

    Keep in mind what a NAS is. It's a computer with a hard drive. Additionally, you have a USB connection hung off of that computer. So, when you plug an external USB hard drive into the NAS, the NAS certainly has the capability of copying directly from the internal hard drive to the USB drive.

    You NAS almost certainly has a web server, which is used for setup. You my find it has a page or tab where you do can file maintainence. So, from that web page you could move files around on the NASs internal hard drive, or between internal and external drives, and the files wouldn't pass through your Mac in this case.

    As well, many (if not most) NASs run some version of Linux. Commercial NAS firmware may or may not expose a Telnet or SSH port and allow you to log-in to a console. If your NAS uses open-source firmware, such as dd-wrt or OpenWrt (also used on routers) then you certainly have this capability. So, you could also log-in through telnet or SSH (recommended the latter and make sure Telnet is turned off, for security reasons) and issue Linux shell commands to do the transfers. Again, these would not need to pass over the network or through your Mac.

    You can even automate backups on your NAS, at least if you are using open source firmware. You will have (or can install) both rsync and cron on your NAS.
  5. jtara macrumors 68000

    Mar 23, 2009
  6. mrbash macrumors 6502

    Aug 10, 2008

    I don't believe this is correct. The NAS would need to have a USB host controller. If the NAS is designed to be connect to a computer via a particular USB port, then that port definitely can NOT be used to attach a salve USB device.

    Remember USB is not Peer-to-peer. It is a Master-Slave interconnect. You cannot simply connect a slave to another slave device. Similarly, you cannot connect a Master to another master and expect it to work as a slave. That is why there is no USB target mode on the mac.

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