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Changing the reported capacity of disk drive

December 29th, 2008 Leave a comment Go to comments

Disk devices that speak the SCSI protocol (SCSI, SAS, Fibre channel, and even USB memory sticks) have a built-in command designed to specify the drive capacity.    The block size and count is defined as mode page settings, so any software product that incorporates a mode page editor has the mechanism to allow you to change the capacity (or block size) of a device.

Why you might want to do this …

  • You have some older equipment running an operating system such as VMS, or certain RAID controllers that have an upper limit on the maximum disk size which they support.
  • You want to be really sneaky and hide information on a disk drive.   (Once you resize the disk, the “hidden” area is hidden from everything, including low-level formats, partition managers, and anti virus software).
  • You are trying to mirror disk drives, and while they are both advertised to be 146GB large, they have a slightly different number of total blocks.   As such, some RAID software won’t let you mirror the two drives.

Security warning — If you do not want to risk data theft, you should always insure that the disks in your storage farm report 100% of their actual capacity before running software to view the contents, or run a secure erase.

Use smartmon-ux -capacity n <drivelist> to set reported number of blocks

Other info:

  • Reformatting is not necessary after changing capacity.  Data is preserved once you restore the hidden area.
  • Even USB flash memory capacity can be changed with smartmon-ux, so you could add two partitions on a USB stick, hide stuff in the 2nd partition, then change capacity as needed to make the partition invisible.
  • smartmon-ux -capacity 0 resizes the disk to factory default, and exposes all hidden areas to insure that somebody isn’t trying to hide anything.
  • More details on usage at http://www.santools.com/smart/unix/manual
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