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Add Mirror

    General discussion

  • When I installed Windows 7 Ultimate to an old desktop that had two Maxtor 7Y250M0 SATA drives, I decided to software mirror the drives.  When I attempted to create the mirror volume, I got a message "there is not enough space available on the disk(s) to complete this operation".  In this case, I was attempting to mirror a volume that used the entire drive.  I did some searches, but couldn't find anything useful about it.  Finally, I just decided to try something and I shrank the size of the volume on the disk I was going to mirror by 1GB, a number I picked arbitrarily.  Then I attempted "Add Mirror" again and it worked.

    I've seen a few articles talking about how to add a software mirror in Windows 7, but they all appeared to be able to set up a mirror for a volume using the full drive capacity without running into the error message I got.  Although I have a functional mirror working now, I thought it would be useful to see if anyone might have any insight as to why I had to shrink the volume slightly in order to get the mirror set up.

    Saturday, April 24, 2010 10:47 AM

All replies

  • On Sat, 24 Apr 2010 10:47:04 +0000, MoritzTechnology wrote:
     
    > When I installed Windows 7 Ultimate to an old desktop that had two Maxtor 7Y250M0 SATA drives, I decided to software mirror the drives. When I attempted to create the mirror volume, I got a message "there is not enough space available on the disk(s) to complete this operation". In this case, I was attempting to mirror a volume that used the entire drive. I did some searches, but couldn't find anything useful about it. Finally, I just decided to try something and I shrank the size of the volume on the disk I was going to mirror by 1GB, a number I picked arbitrarily. Then I attempted "Add Mirror" again and it worked.
    >
    > I've seen a few articles talking about how to add a software mirror in Windows 7, but they all appeared to be able to set up a mirror for a volume using the full drive capacity without running into the error message I got. Although I have a functional mirror working now, I thought it would be useful to see if anyone might have any insight as to why I had to shrink the volume slightly in order to get the mirror set up.
     
     
    RAID 1 (mirroring) is *not* a backup solution. RAID 1 uses two or
    more drives, each a duplicate of the others, to provide redundancy,
    not backup. It's used in situations (almost always within
    corporations, not in homes) where any downtown can't be tolerated,
    because the way it works is that if one drive fails the other takes
    over seamlessly. Although some people thing of RAID 1 as a backup
    technique, that is *not* what it is, since it's subject to
    simultaneous loss of the original and the mirror to many of the most
    common dangers threatening your data--severe power glitches, nearby
    lightning strikes, virus attacks, theft of the computer, etc. Most
    companies that use RAID 1 also have a strong external backup plan in
    place.
     
    "Why RAID is (usually) a Terrible Idea"
    http://www.pugetsystems.com/articles?&id=29
     
    Ken Blake, Microsoft MVP (Windows Desktop Experience) since 2003
     

    Ken Blake
    Saturday, April 24, 2010 6:17 PM
  • Ken,

    Your answer is completely useless and does not address the original post at all.  In fact, it is completely irrelevant.  The poster didn't ask about proper backup strategy.

    I am also having this same problem where I get an error message "There is not enough space avaialbe on the disk(s) to complete this operation" when I try to mirror a drive.  I have two identical drives, one is completely unallocated while the other has a single partition taking up the entire disk.  The disk I am mirroring to is empty, so I can't imagine that the error message is referring to that disk.  The disk with data is almost completely full.....I've tried moving some data off and now have 34GB free of 698GB, but I still get the error.  Do I need to keep moving data off to create more free space or is this a red herring?  If so, how much free space is needed?

     

    Wednesday, November 3, 2010 10:38 PM
  • Thanks for sharing your tip. I shrank my drive by one 1GB and now I am able to mirror it. Thanks!

    Tuesday, March 22, 2011 6:07 PM
  • Thanks Mortiz! I only needed to shrink 100MB's. And Ken, that was a completely useless post and had zero relevance to what he was asking. 
    Friday, April 22, 2011 8:20 PM
  • I've just had the same problem with Win7 (Pro 32b) and the same solution worked.  In my case the two disks, tho both nominally 500GB, were different types so there may have been some slight size or organisation mismatch between them.  Thanks for the tip tho.
    Saturday, April 23, 2011 6:03 PM
  • Info in How to mirror the system and boot partition (RAID1) in Windows Server 2003 -

    Upgrade to dynamic disks

    RAID systems require dynamic disks in Windows Server 2003. Any disks that you are upgrading must contain at least 1 megabyte (MB) of free space at the end of the disk for the upgrade to succeed. Disk Management automatically reserves this free space when it creates partitions or volumes on a disk, but disks with partitions or volumes that are created by other operating systems may not have this free space available.

    So, shrinking the partition by 1MB should be enough.

    Thursday, February 23, 2012 5:03 PM
  • Hey,

    Just had this error.

    Now what I did was to convert the disks to MBR and then to GPT, mirror was then possible.

    I have done this with two 1TB drives.

    All the best!

    Thursday, June 14, 2012 5:47 PM
  • I ran into this on Server 2012 R2... It is now April 2nd, 2015 and it still continues.

    Even with identical drive, if you have ever added and removed a volume then you are shorted a couple of MBs of space in the eyes of the system.  This keeps you from mirroring the volumes on primary drive if the volumes have been setup to take up the entire drive.  This catches most admins off guard accustomed to hardware RAID and just throwing a like make and model drive in and calling it good.

    Taking a drive that is new from the vendor or has just been clean wiped using the hard drive manufactuer's utility or DBAN (zero write) then you can just mirror and go.  Just like in the videos or the manual.

    If you have ever added or deleted volumes of the drive you want to mirror to, you must clean wipe this secondary drive and then use it or do the trick others spoke about in the thread and reduce the volume size of one of the volumes on the primary drive by a couple of MB.... 2MB did it for me.

    I've tested this with both magnetic and SSD drives of exactly the same make and model and with nominal space in serial numbers.  All drive utilities show them as having exactly the same space down to the 'ones' digit byte.

    A different Ken...


    Thursday, April 2, 2015 10:23 PM
  • Woohoo!   Thank you, I could not figure out why the 'Add Mirror' was grayed out on my 2nd partition after the mirror on the 1st partition; shrinking the 2nd partition by 1MB did the trick!!
    Thursday, October 13, 2016 2:21 PM
  • I tried reducing the size of the partition that I wished to mirror with no luck. (I reduced it by many gigabytes with no success.) I finally got EaseUS Partition Master and converted the drive that I wished to mirror to from dynamic to basic and then used the Delete All command to delete everything on that drive. Then the stupid "there is not enough space available on the disk(s) to complete this operation" error went away.

    Note that I am running Windows 10 Pro.


    Friday, April 19, 2019 9:18 AM