VTOC , EFI disk label comparison
A disk lable is a special area for storing information about the disk’s controller, geometry, and slices (or partitions). This information is called the disk’s label and in Unix its called volume table of contents (VTOC). Writing slice information onto disk is called labeling a disk. Before label a disk you have to define its slices.VTOC is widely used in Solaris and it support less than 1TB of data. EFI ( Extensible Firmware Interface) is a new type of disk label which support disk that are larger than 1TB and cannot be converted back to VTOC.
Solaris supports both types VTOC disk label and the EFI disk label. Solaris 10 (and later versions of Solaris 9) provides support for disks that are larger than 1 TB on systems that run a 64-bit Solaris kernel. The EFI label provides support for physical disks and virtual disk volumes. The UFS file system is compatible with the EFI disk label, and you can create a UFS file system greater than 1 terabyte.
The traditional VTOC label is still available for disks less than 1 terabyte in size. You can use the format-e command to label a disk less than 1TB with an EFI label.
The advantages of the EFI disk label over the VTOC disk label are as follows:
- Provides support for disks greater than 1 TB in size.
- Provides usable slices 06, where slice 2 is just another slice.
- Slices cannot overlap with the primary or backup label, nor with any other partitions. The size of the EFI label is usually 34 sectors, so partitions start at sector 34. This feature means that no partition can start at sector zero.
- Sizes are reported in blocks. No cylinder, head, or sector information is stored in the EFI label.
- Information that was stored in the alternate cylinders area, the last two cylinders of the disk, is now stored in slice 8.
- If you use the format utility to change partition sizes, the unassigned partition tag is assigned to partitions with sizes equal to zero. By default, the format utility assigns the usr partition tag to any partition with a size greater than zero. You can use the partition change menu to reassign partition tags after the partitions are changed.
- Solaris ZFS uses EFI labels by default.
But there some restrictions with EFI disk labels and those are:
- You cannot boot from a disk with an EFI disk label.
- The EFI disk label is not supported on IDE disks.
- The EFI specification prohibits overlapping slices. The entire disk is represented by c#t#d#.
- The SCSI driver, ssd or sd, currently supports only up to 2 terabytes. If you need greater disk capacity than 2 terabytes, use a disk and storage management product such as Solaris Volume Manager to create a larger device.
- Layered software products intended for systems with EFI-labeled disks might be incapable of accessing a disk without an EFI disk label.
- You cannot use the fdisk command on a disk with an EFI label that is greater than 1 terabyte in size.
- A disk with an EFI label is not recognized on systems running previous Solaris releases.
- You cannot use the Solaris Management Console’s Disk Manager tool to manage disks with EFI labels. Use the format utility to partition disks with EFI labels. Then, you can use the Solaris Management Console’s Enhanced Storage Tool to manage volumes and disk sets with EFI-labeled disks.
- The EFI disk label provides information about disk or partition sizes in sectors and blocks, but not in cylinders and heads.
- The following format options are either not supported or are not applicable on disks with EFI labels:
- The save option is not supported because disks with EFI labels do not need an entry in the format.dat file.
- The backup option is not applicable because the disk driver finds the primary label and writes it back to the disk.
If you have volume manger VxVM EFI disks wont work under Solaris 9. But Solaris 10 supports. Its in fact VxVM is not supporting as you could label, create ufs filesystems on these disks and so on. But when you do vxdisksetup you will get errors.
Ref : Sun Docs, Veritas Docs