Time Machine-friendly HDD images

Discussion in 'Feature Suggestions' started by mjs, Mar 23, 2008.

  1. mjs

    mjs

    Messages:
    26
    Hi,

    I'd like to see Time Machine friendly HDD images. A HDD image should be a sparse bundle or something like that. If it's impossible to use sparse bundles together with the snapshot feature then you should think about a HDD bundle where the image is split into many small files (128MB or even smaller?). This would allow a user to use Time Machine with backup drives over WLAN.

    EDIT: Sparse bundles use a default file size of 8MB - but I think that this might be too small.

    Regards,
    Mark
     
  2. rekoil

    rekoil

    Messages:
    5
    Not sure what the performance implications of this would be, but the ability to only back up the "changed" parts of a virtual disk image could be compelling. Since the image file represents a physical device, however, there are some problems with this.

    Theoretically, one could create an automounting sparsebundle and symlink the Parallels directory to it, then have Time Machine back up the sparsebundle but exclude the Parallels directory. This could emulate the desired behavior, only backing up modified bundle files which (I believe) correspond to physical "chunks" of the virtual disk.

    The main problem with this is that Windows, like MacOS, most likely moves files around the physical disk a lot in the background. A defragment routine is a great example and would most likely result in the majority of the disk's sectors being changed, triggering a backup of most files in the bundle even if no files themselves were modified.

    Interesting problem - not without potential solutions, but those solutions may sacrifice performance to the point that it's not worth it.

    For my part, I use the home directory share to store all files I use in Parallels, so Time Machine backs them up normally. This obviously doesn't help with installed applications, but those can always be re-installed if needed.
     
  3. Eru Ithildur

    Eru Ithildur

    Messages:
    1,966
    It would be a very useful feature, and has been brought up before. As rekoil pointed out, the performance is a major issue with implementing this, though.
     
  4. woferry

    woferry

    Messages:
    6
    I recently asked for the same feature (RT #620190) and was pointed at this forum. Both my copy and my mother's copy have around 6GB images, and they consume a large portion of the TM space because every time TM is launched it causes TM to have to back up the entire image. In my parent's case their back is done over wireless to a Time Capsule, and it takes over 80 minutes to push the 6GB over a 5GHz 802.11n-only network, which is very painful.

    It turns out that there is already support for 'Segmented' images and the .xml file inside the .hdd bundle even defines the size of each segment, but currently the only allowed segment size in the Image Tool is 2GB. So I could split both of our images into 3 chunks, though every time Windows starts all of the chunks get touched, I'm not sure whether this is a bug in Parallels or if it's simply that with the chunks being so large Windows has a good chance of touching files in all of them.

    If there was at least an option to select a smaller chunk size (either via a 'defaults write' or an actual GUI) it would at least allow experimentation. I personally don't buy the performance excuse, I haven't seen any noticeable performance hit in Mac OS X's sparsebundle disk images after switching to them for non-Parallels tasks. Even 128MB segments might make a big difference in TM performance, though since Mac OS X defaults to an 8MB band size I'd sure like to try that segment size in Parallels as well even if there was a tiny performance hit, for what my parents and I use Parallels for disk I/O is not that important, but not losing data is very important, and having to leave the machine running for extra hours after finishing up in Parallels is not good.

    Thanks. - Will
     
  5. John@Parallels

    John@Parallels

    Messages:
    6,450
    Please understand that we do not recommend to use Time Machine with Parallels Desktop
    The best way to backup Virtual machine is to clone it, or simply copy VM bundle (v4) or VM folder to backup location
     
  6. woferry

    woferry

    Messages:
    6
    That unfortunately is a terrible response. Suggesting against using what has to be the easiest-to-use backup software in the world is just lame. Fixing whatever bug in theory prevents Parallels from working with it would seem to be the correct solution. Most Mac software companies are *embracing* Time Machine, not recommending against it. The last thing my parents need is another (more complicated) backup solution for a single application.
     
  7. John@Parallels

    John@Parallels

    Messages:
    6,450
    This is not a bug, this is design, which allows you to get most performance from your Mac
    You can use Time Machine, but when VM is in stopped state
     
  8. woferry

    woferry

    Messages:
    6
    That's exactly what I'm doing, except pushing 6GB over the network takes over an hour after Parallels has been shut down (I already said this). If Parallels supported smaller segment sizes like Mac OS X's .sparsebundle disk images (8MB vs. Parallel's current 2GB minimum segment size) then I would hope that Windows wouldn't be modifying all of the chunks every time it is launched and then TM wouldn't have to push 6GB of data every time, saving both time to backup and space on the TM drive. Unfortunately with 2GB segments I do see all 3 segments get touched every time (just launching Windows and shutting down as soon as it's finished booting), so I'm not sure if it's just the fact that files Windows always touches span all 3 segments, or if Parallels itself is touching the segments for the fun of it. If the latter then even 8MB segments obviously wouldn't help if they all got touched every time.

    Thanks. - Will
     
  9. mydanes

    mydanes

    Messages:
    66
    ACTUALLY, using TM or ANY OTHER backup software with Virtual Machines is pragmatic for the very reason that they 'change' every time you use them thus they require backup EVERY time you access them. I manage MANY VM environments and I backup at key points to a 'file' and let that go to TM and since I don't actually run the copy it is copied ONCE 'not every time TM runs'.

    Just another idea for you!
     
  10. Brian McGroarty

    Brian McGroarty

    Messages:
    2
    The ideal solution, I think, would be to allow Time Machine to exclude only the undo disk, while still backing up the underlying disk. Then Time Machine would not back a VM while a VM is being used. But any time a user elects to save the changes back to the underlying disk, then and only then is there a lengthy Time Machine backup.
     
  11. Jesper ordrup

    Jesper ordrup

    Messages:
    2
    How about allowing Time Machine to backup any virtual disk as a regular os x disk. This would then allow for filebased backups.

    I guess what is needed is some extra functionality to Parallels to allow disk access even when the virtual maschine is not running or?

    Add to basket..

    Thanks
    Jesper
     
  12. JessC

    JessC

    Messages:
    1
    Hey Guys,

    I would like to be able to backup SOME files of the Parallels' virtualised OS with time machine and NOT the full windows or other OS. This would save a lot of time in a daily backup and face it, sometimes we just need ONE base snapshot and only incremental DATA to adjust our applications we need in our non-mac os .
    thnks
     

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