Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I need to clone my 300GB disk to 500GB disk with dd, but the old disk (300GB) has too *big block size.

Will this change the block size of output partition too? I understod that obs only meant to be used during copying, and would not change the partition block size?

dd if=/dev/hda of=/dev/hdb obs=4096

Note that this hda contains only one NTFS partition with Windows 7 installed which I try to clone to the new disk.

*I chose too big block size when I thought I can put only vmware images on the drive. But that did not happen since main OS disk failed sometime ago and now my OS is on disk that has a huge block size.

share|improve this question
up vote 1 down vote accepted

Create NTFS partition on /dev/hdb(with -c option) and copy file from /dev/hda. block size is set when you create the filesystem, dd can't change block size.

   -c, --cluster-size BYTES
          Specify the size of clusters in bytes. Valid cluster size values are powers of two, with at least 256, and at most 65536 bytes per cluster. If  omit‐
          ted, mkntfs uses 4096 bytes as the default cluster size.
share|improve this answer
Good to know, I will mark this as answer... but since you are here do you happen to know how can I copy all files and MBR to make the new disk bootable? – Ciantic Feb 4 '11 at 17:06
You can use dd to copy partition and Acronis Disk Director to resize clusters. – alvosu Feb 4 '11 at 17:14

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.