Introducing AX64 Time Machine - hybrid imaging/snapshot software

Discussion in 'backup, imaging & disk mgmt' started by Isso, Jan 18, 2013.

  1. manolito

    manolito Registered Member

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    I believe that the behavior of any VSS based image backupper in this situation (starting a backup while being in the middle of a download) depends entirely on how the VSS itself handles it.

    Obviously while downloading the target file is open for writing and cannot be locked by the VSS. AFAIK there is a timeout for the locking process, and after this timeout the VSS will give up so the download target file will not be a part of the VSS snapshot. Which of course means that this file will not be backed up.

    I am not all too familiar with the Windows VSS system, so someone who is please correct me if necessary...



    Cheers
    manolito
     
  2. MaximumFish

    MaximumFish Registered Member

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    I use Crashplan to backup my critical files, documents and the like. I wanted Time Machine to be something that acts much like the Mac version does, something that will let me do a full system restore without the need to make full disk images for every backup. As far as I can tell, only AX64 offers that kind of functionality, right?
     
  3. Peter2150

    Peter2150 Global Moderator

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    No it's not a weakness with auto snap. Sometimes one has to apply the software between the ears. I used to run Shadowprotects Continuous incrementals, which was very versatile. I took 15 min incrementals. For updates, it was simple. Suspend or turn off the incrementals and do the updates. With AX64 I prefered auto snaps from 9 in the morning until noon, but I didn't want auto merge. I was able to do this by turning on auto at 855 and turning it off at 1205. It did work, but too easy to forget. With TM I can't do that because it was combined with the multi partition, which I can't use on my systems. Hopefully Waj and company realize that was a huge mistake.
     
  4. bgoodman4

    bgoodman4 Registered Member

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    All software is fallible,,,,including that between the ears.

    I guess, from the lack of comment, that the idea does not bother folks. Snaps during a download seems to be of more interest, not sure why that would be. In my case before I do an install I always do a manual snap (MS update has to ask before it can install) so I do not expect to run into this problem, but given AX64/TMs main target audience I can see where the app would simply run, ignored, until a rollback was needed. It is under this circumstance that the problem could arise. Personally I am curious what would happen but am not interested enough to try it on my PC. Maybe someone will find the thing interesting enough to test on a VM, if so that would be great.
     
    Last edited: Jun 8, 2014
  5. MaximumFish

    MaximumFish Registered Member

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    Yes, I'd also be very interested to know what would happen, but with a system update I'd expect a broken restore. Of course if auto-snap is on then the hour's backup on either side would be fine.
     
  6. taotoo

    taotoo Registered Member

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    I like manolito's answer. Presumably VSS is designed to deal with exactly this issue.
     
  7. Peter2150

    Peter2150 Global Moderator

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    Presumably isn't a good answer. A while back I wondered what would happen to a couple of office type programs if the machine crashed. Well only one way to find out. First I did a backup. Then I opened the programs and made and easy to spot change in each, leaving both programs open. Then I did a power reset. That make a good crash. Having done that I reopened the programs, and in both cases the changes were there. Now there is no longer an wondering or presumptions. I know.

    If you want to know what will happen on your machine with the question in hand the only way to know for sure is to try it.

    Pete
     
  8. taotoo

    taotoo Registered Member

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    I think we do effectively try it every time we make a backup with software that relies on VSS. It's not just 7gb files that the issue applies to...
     
  9. Rainwalker

    Rainwalker Registered Member

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    Greetings..I stupidly installed V.2 over V.1 when it hit the fan. Computer slowed down and later found itself, but the WD My Passport I was using for backups went south. It would not show up anywhere I could see (Device Manager & under Computer on Start Menu. It would blink(as it does) a few times then go to solid blue. Tried all my USB ports and it was the same. Checked USB ports with flash drives and they worked fine. Thought My Passport got fried so got a new one only to see same thing. Very strange. Anyone with possible help?
     
  10. Baldrick

    Baldrick Registered Member

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    Hi Rainwalker

    Sorry for stating the obvious (to me)...but have you tried using the Recovery CD (assuming that you made one) as AX64 run from there may well pick up the external drive as part of its recovery preparations?

    Just a thought.

    Regards, Baldrick
     
  11. Rainwalker

    Rainwalker Registered Member

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    In trying to fix my issue I uninstalled v.2 and then reinstalled v.1. Before installing v.1 I ran PrivaZer. Tried the backup you mentioned anyway, but no good. I thought PrivaZer would have cleaned out any bits that might be causing the problem, but....why would My Passport not be showing itself when other flash drives do while using same ports o_O
     
  12. bgoodman4

    bgoodman4 Registered Member

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    No, in this case I think it may not be. As I understand it VVS will lock the drive as it exists at a specific time and then the back-up or image will proceed. How it can do that in the middle of an install and still allow a snap to proceed on time (which in this case is 1 min after the hour) is an open question. If AX64/TM waits until the install is completed and then VSS is effected then yes, all is well. If not, then the potential for a real problem is present. As Peter said, the only way to know for sure is to try it, or perhaps a comment from the developer would clear things up. For the moment I think its still an open question.
     
    Last edited: Jun 9, 2014
  13. bgoodman4

    bgoodman4 Registered Member

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    It may be that the drive has lost its designation (D: or whatever). I ran into this issue some time ago and perhaps the solution I found on-line will help in your case. The following is exactly as I copied it from wherever I found the ans to my problem.

    To change external drive from off-line to on-line

    First open Disk Manager:
    - Start -> right-click "Computer" and select "Manage"
    - click on "Disk Management" in the left pane.
    - find the partition in the lower-right portion of the right pane, click on the drive that is off-line (left part where it says offline) and right click, then select "On-line"
     
  14. Brian K

    Brian K Imaging Specialist

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    Rainwalker,

    Try assigning a drive letter in Disk Management.
     
  15. manolito

    manolito Registered Member

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    I found many very technical explanations on how VSS works, this one is the easiest for me:
    http://blog.macrium.com/2012/11/backup-internals-what-is-vss-how-does-it-work-and-why-do-we-use-it/

    Taken from this blog:
    This means that if a backup starts in the middle of a download or of a software installation, only the data which have already been written at the time the VSS snapshot is created will be included in the snapshot. Once the VSS snapshot is complete (less than 10 sec) the download or the installation will proceed normally. They will just not be included in the backup.


    Cheers
    manolito
     
  16. bcw

    bcw Registered Member

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    My idea is also to use another imaging program for full backups, but to use TM for regular snaps. On my work PC, I have a USB drive connected on the port replicator so it is constantly being disconnected/reconnected as I go to meetings and return to my desk. I have found the TM program has appeared to lock up a couple of times already (i.e. today it reached 95% and then just sat there).

    Eventually I killed off AXTM program to start it again. Is this only the front end application, or does it also kill off the tracker? What program is running the tracker, and how do I know if it stops? Obviously if the tracker stops or misses some changes, then an image may not have all data, and a restore using it may not be complete. If the backup gets stuck, what is the best action to take?
     
  17. TheRollbackFrog

    TheRollbackFrog Registered Member

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    BCW, the tracking capability never stops once installed and remains that way until the entire app is unINSTALLed. The tracking is done by an installed driver, not by any additional coordinated process. It matters not if the AXTM app is running or not.

    If the backup gets stuck (it really shouldn't do this unless there's a storage elemenet problem) and you have to kill the process, it will leave a .TEMP file in the backup folder. This can be deleted if you wish... just make sure AXTM isn't running at that time. Some have reported that if left in place, sometimes the next backup process saves an entire baseline once again. I have never seen this happen and have killed AXTM during backups many times, leaving those .TEMP files in place for further testing. This baseline restart anomaly may be a v2 thing... I haven't tested that yet under v2.
     
  18. bgoodman4

    bgoodman4 Registered Member

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    And therein lies the problem. If you need to revert to that snapshot then you will be booting to a PC with an incomplete installation of the software. The download situation does not concern me as its simply a matter of re downloading the files. It may well be more of a problem booting the PC if a critical (OS) update was being installed at the time of the snap.
     
  19. Rainwalker

    Rainwalker Registered Member

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    Thanks for getting back Brian K & bgoodman4....I had tried your suggestions prior to posting. I cannot see the Passport drive in Disk Management so..... I can see it now in Device Manager under Universal Serial Bus controllers. Any other thoughts?
     
  20. SanyaIV

    SanyaIV Registered Member

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    Would it perhaps be possible for AXTM to detect if Windows is installing any updates or if a program is installing and if something like that is detected then postpone the backup until the update/installation in question is done? I'm guessing maybe it can detect such things? I'm guessing it mostly on the fact that some installers can detect that another installer is in process (or uninstallation for that matter) and tells us to finish that one first. However maybe it would be hard to do and/or not be useful enough for the coding needed and perhaps it wouldn't be useful at all and I'm guessing it could also bring false positives, i.e it thinks something is installing but there isn't? ... Iunno, may or may not be possible/useful, just had the idea.
     
  21. Isso

    Isso Developer

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    Hi BG, folks

    No worries, the system won't allow to create a VSS snapshot while it's in critical update phase (that's happening either on system shutdown or boot-up). Overall VSS works quite well (when it works), and I've never seen any snapshot that left the system in an unstable state.

    Isso
     
  22. TheRollbackFrog

    TheRollbackFrog Registered Member

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    It's called doing business. Any snapshot or "automatic" imaging application (Rollback RX included) has this issue. All the automatic imagers that I'm aware of mostly use VSS when locking the system, and some that don't, use their own mechanism (IFW using PhyLock) which suffers from the same problem... a locked system at storage time. It's NOT a problem, it's a way to freeze the system while the backup (or snapshot) is being taken and provide for a "consistent" file state when operating. Without it would be pandemonium as far as file states are concerned (and some backup programs do this without VSS).

    VSS was designed to allow this consistency to be handled by the applications producing the data if they felt it was important... it's up to the app doing the file writing to make that decision, not the app doing the reading. If an app feels that its file consistency is very important (just about any good database does), it asks Windows to let it know when anyone is freezing the file system... Windows will do this if asked. Windows warns the app that a freeze is coming, the app puts its house in order as far as file consistency is concerned, then the file system lock occurs. If the app doesn't feel its file consistency is important, it winds up with an inconsistent point in time as far as its manipulated data is concerned.

    It's really not up to AXTM to insure consistent data on the system... it does its very best by invoking VSS and warning data producers of the impending freeze, it's up to the producers to insure consistency if they feel it's important.

    Remember, all your favorite imagers work in the same way... Macrium, IFW, etc. If you're running automatic imaging intervals, it can happen at any time.
     
  23. SanyaIV

    SanyaIV Registered Member

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    So AXTM/VSS locks the system when taking a snapshot? I don't really understand how this works, why can I still create files during a snapshot then? =S

    But what I was thinking is, lets say the time is 12:59 and you start an installation of a new program, lets say that installation doesn't finish until 01:02, if AXTM was on automatic then it would take a backup at 01:00, right? Wouldn't that mean that half of the installation would make it into the backup but the rest wouldn't? How would the installer itself be able to change this outcome?

    With my idea in my last post, AXTM would notice the installation at 01:00 and then it would wait for it to finish, so the new backup would be taken at 01:02 or something like that, I was just wondering if that would be possible and if that would improve this situation? Or is the situation itself imaginary and taking a snapshot during an installation can cause no corrupt installations at all? (when restoring the relevant snapshot I mean)

    Sure it may be an issue relevant to all similar applications but does that mean there's no reason to look into fixing it? Or is it like I asked before, not really an issue at all?

    Personally I don't care because I don't use the automatic backups.
     
  24. TheRollbackFrog

    TheRollbackFrog Registered Member

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    What happens when a lock is placed on the file system is that any further WRITEs are forbidden to the actual file system... those WRITEs occur into a temporary CACHE. When running in this mode, any READs of data that have not changed since the lock, will occur out of the locked file system, other READs of data that have changed, occur out of the temporary CACHE. When the lock is released, Windows "merges" the temporary CACHE to the now unlocked file system and all is whole once again.

    I would think it to be very difficult for an app to determine if another app was installing something... what is an install but mostly a bunch of file writing and registry entering. This stuff is done all the time by apps not installing anything. And why just worry about installs... what about all the other incomplete data being written to the system.

    As Isso says, the VSS system works pretty well... when it works (it's know to have some "anomalies" occasionally). And as I mentioned above, it's up to the app doing the writing of the data to insure consistency, not the reader.
     
    Last edited: Jun 10, 2014
  25. TheRollbackFrog

    TheRollbackFrog Registered Member

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    I, personally, don't know the mechanism that's used to allow for the consistency to be maintained, but it's always used during BOOT up and TAKE DOWN... and apps that require consistency use it to insure they have the time to get their data consistent. It must be a simple mechanism... the app says lemme know when you want to freeze the system and I'll let you know when I'm consistent. When that handshake has occurred between Windows and all the apps that want to be consistent, Windows will issue the LOCK to the requesting application (AXTM) and it may now do its thing.
     
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