Macrium Reflect very slow differential backup but very fast verify

  1. Posts : 32
    Windows 10 64-bit Pro

    Macrium Reflect very slow differential backup but very fast verify

    So today I tried to use Macrium for the first time.
    I first made a full windows restore backup that took 56mins to finish and right after that made a Differential image that took 41mins to finish.
    The full backup files size is 113gb and the differential backup file size is 1,7gb.
    How is it that the differential backup took almost as much time as the full backup to finish even though the file size is that much different.
    Also, as the titles says, when macrium verified the differential bckp image it took only 30s to complete when for the full backup image it took about the same time to verify it than to make it.

    I am using a WD Elements external HDD to store the backups, plugged-in trough a USB3.0 port and the reported data rates for full and differential are respectively "Read 2.0 Gb/s - Write 598.5 Mb/s" and "Read 1.5 Gb/s - Write 495.8 Mb/s"

    Thanks in advance for any help.
      My Computer

  2. Posts : 43,249
    Win 10 Pro (22H2) (2nd PC is 22H2)

    I think the answer to why verification is so fast is because it isn't doing what you think it might be doing. See:
    Verify Image
    Verifying image and backup files - KnowledgeBase - Macrium Reflect Knowledgebase
      My Computers

  3. Posts : 30,287
    Windows 11 Pro x64 Version 23H2

    Hi Lantha

    Maybe this will help.

    They don't state how this comparison is accomplished but data in and out over USB likely adds to delay.

    Verifying is likely not what you think it is. Read the first line of this. It is not comparing data back to original.
      My Computer

  4. Posts : 32
    Windows 10 64-bit Pro
    Thread Starter

    First, thanks already for your help
    Now, I understand for the "verifying" part but, other than that, the following numbers just don't add up :
    Full: || Differential:
    Read 2.0 Gb/s - Write 598.5 Mb/s || Read 1.5 Gb/s - Write 495.8 Mb/s
    113gb || 1.7gb
    56mins || 41mins

    Is it because there is more calculations and operations involved in the creation of differential backup ?
    Last edited by Lantha; 05 Oct 2018 at 14:13.
      My Computer

  5. Posts : 30,287
    Windows 11 Pro x64 Version 23H2

    It has to be how they do the comparison. I imagine they can't just work off the file flags to say this has been backed up. They even say as you get further away from your full the longer it will take.

    You could post on the Macrium forum and ask how the comparison works.

    This is not about how much data it wrote, it is about how long it took to figure out what data to write.
      My Computer

  6. Posts : 1,871
    W10 pro x64 20H2 Build 19042.610

    I've noticed in the past (when I used Macrium for a while) that differentials take a surprisingly long time, pretty much the kind of ratio you are seeing. I've also noticed the same thing with AOMEI in that both incrementals and differentials are also not that much quicker than a full image.

    Many years ago I used to use Acronis (I wouldn't recommend that product now for various reasons) but I do seem to recall that incrementals (I never used differentials back then) were extremely quick and of the order of just two or three minutes compared to perhaps 30 minutes for a full image.
      My Computer

  7. Posts : 32
    Windows 10 64-bit Pro
    Thread Starter

    I can't post on their forum because I didn't buy any licence key but I think Caledon Ken spotted the cause anyway.
    Thanks for the help, marked as solved

    EDIT: I'll check out Acronis, thanks
      My Computer

  8. Posts : 32
    Windows 10 64-bit Pro
    Thread Starter

    I freed up some space on my external HDD and now it's running fast and completes within 3mins. I think it was working slow because:
    1. I had less than 5gb left on the hdd
    2. I had configured the minimum free space size limit to 5gb (it deletes the oldest differential backup image if there is not enough space to store a new one) and in my case there was already not enough space for a new image
    3. And finally, apparently, if it's impossible to make a new differential image (in my case because there is not enough space), macrium will instead do a new full backup (strangely, it still made a small sized file but it took the time of a full backup image to make it) You can see they notify you about that when you go in the "backup definition files" tab, you right click on any of them, click on "run now" and then "prompt..." (bottom line in the window that pops-up)

    Another theory is just that macrium needs more free space to run fast.

    In the log files there is a difference between the ones from the slow differential backups and the ones from the fast differential backups.
    Even though the two sides say that they are in differential mode, the fast ones say :

    Saving Partition - OS (C:)
    Reading File System Bitmap
    Looking for changes
    Saving Partition
    When the slow ones only say :

    Saving Partition - OS (C:)
    Reading File System Bitmap
    Saving Partition
      My Computer

  9. Posts : 43,249
    Win 10 Pro (22H2) (2nd PC is 22H2)

    Mm, good observation. A MR backup task allows you to specify the max number of base and differential images to be retained. Thus for example if you choose to keep up a max of 5 diff. images, when you get to 6, the first is deleted. (You only need 1 base + 1 corresponding diff. image to restore).

    This gives you an idea of the max space required once you know the size of base image, assuming the used space doesn't change that much, or at worst, the size of the partitions being imaged.

    The size of an image also depends on whether the files being imaged are already compressed.

    Thus planning your required disk image storage should be reasonably practicable with due allowance. Unfortunately I've not seen any way MR supports such an estimate.
      My Computers


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