Windows Backup slow after extending volume

solplus
solplus used Ask the Experts™
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We have an HP ProLiant ML350G6 running Hyper-V with 6x146GB disks in a RAID5 array. Due to a shortage of space we extended the array by adding another 2x146GB disks. This went well. However we are now running the first Windows backup (Windows Server 2008) on the disk array since we increased the volume from 500 to 700GB and it is taking a long time to backup. It is part way through and we estimate it will take 30 hours to complete. A full backup would have normally taken 7 hours. Should it take so long?
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You didn't give a full timeline but when you expand an array it has to rebulid the set.  Depending upon size/speed/usage, this could take hours to days.  Was the rebuild done when the backup started?

Author

Commented:
Thansk for the prompt response. Yes the rebuild was done when the backup started.
Did you reboot the system when done with the rebuild?  I'm not aware of any specific issue why it would have trouble with a bigger disk.  More details might help others though.

Is it Windows Backup or another software backing up Windows?

How was the array increase presented to Windows?
Does it see it as new free space unpartitioned?
Did the partition increase appear as new free space within a Windows drive?
If that's the case I would dig into the HP Array manager for issues, Windows has no idea what the drive is doing, just that is has been presented some space.
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Author

Commented:
Yes we rebooted the system.
It was Windows Server Backup.
A partition on one of the virtual servers was extended via Disk Manager.
Yes the additional space appeared as free space within the partition which hosts the virtual disks.

I suppose the big question is, when you extend a a partition does Windows Backup then decide it must backup the whole volume rather than the incremental changes which it would normally backup? If so would this slow backup be the only one and subsequent backups revert to a few hours?
Thanks
I wouldn't think so, bit level backup of empty space?
Commented:
The backup actually completed in 19 hours, but subsequent backups have been between 7 & 8 hours, so it must have been imaging the whole volume after it had been expanded. Presumably as it redistributes the data each block is modified and so requires to be backed up.

Author

Commented:
Have to assume that the answer was just that it was updating the whole backup image.

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