Non-standard Disk Sizes and Linux

Actual disk sizes (to the byte level) vary from vendor to vendor. Therefore, for the purpose of generalization, N1 Provisioning Server assumes the size of all disks to be 30*10 ^9 bytes or 30GB. However, the actual disk size of B100n blades is slightly more than 30*10 ^9 bytes (30005305344 bytes). Therefore, a disk image of 30*10 ^9 is guaranteed to work on all B100n/B200n server blades and a disk image of the actual size of the disk might not work on all server blades (due to the variance). Using a disk size value of 30*10 ^9 bytes for all images created ensures that the image will be deployable on all server blades.

The Linux operating system uses disk blocks towards the end of the disk also to store its data. As a result, taking a 30*10 ^9-byte snapshot of the disk leaves out a few critical disk blocks that are towards the end. A blade provisioned with this image will fail to boot. To solve this problem, create a dummy filesystem (approximately 10 MB to account for the extra bytes) towards the end of the disk and exclude this file system before taking the snapshot.

The following disk partition is one example:

part /--asprimary --fstype ext3 --size 512 --grow --ondisk hda 
part swap --size 2048 --ondisk hda 
part /tmp --fstype ext3 --size 512 --ondisk hda 
part /dummy --fstype ext3 --size 10 --ondisk hda 

Notice the /dummy filesystem of size 10 MBytes in the partition information.