Disk Initialisation – SMI Label vx EFI Label

Whenever we detect a new disk in Solaris operating system, the first operation we perform is “Disk label” using the format command. The purpose of this post is to explain the background information of Solaris default disk labeling and also discuss the EFI disk labeling introduced from Solaris  9 and later Versions.


SMI Label:

Default Solaris Disk label , i.e. VTOC ( Volume to Content Table) aka SMI(Sun Microsystems, Inc)  label, contains the information such as logical partitioning, disk geometry and other access characteristics. 

In Sparc Hardware – Disk Label ( or VTOC) resides in the first sector ( 512 bytes) of the disk or logical unit. If we run the format command , first time after a  disk was recognized in the operating system, the format command will look at this first sector and complain about “Missing Label” in case of missing VTOC table.

# prtvtoc /dev/rdsk/c0t1d0s2

* /dev/rdsk/c0t1d0s2 (volume “gurkulDisk”) partition map


* Dimensions:

*     512 bytes/sector

*     133 sectors/track

*      27 tracks/cylinder

*    3591 sectors/cylinder

*    4926 cylinders

*    4924 accessible cylinders


* Flags:

*   1: unmountable

*  10: read-only


*                          First     Sector    Last

* Partition  Tag  Flags    Sector     Count    Sector  Mount Directory

0      2    00          0   7788879   7788878

1      3    01    7788879   2100735   9889613

2      5    00          0  17682084  17682083

7      8    00    9889614   7792470  17682083


Backup Label:


Every time we label a disk there will be backup label that will be created on the same disk.

The backup label, or rather, labels, are stored in the last “reserved cylinder” or “alt” cylinder, but in some very old disks they were put in cylinder 2. There are always 2 “alt” cylinders , the last one houses the defect list and the backup labels. The defect list is store in the first 5 even sector, while the backup labels are replicated in the first 5 odd sectors.

Since the “alt” cylinders cannot be part of any partitions, they are not accessible directly through device file interface (i.e. you would hit EOF before you can reach the alt cylinders). The format utility or extended ansi library functions like write_vtoc() calls the device driver through ioctl() directly to access those areas.

When doing “format -> label”, both the primary label (on block 0) and the backups are written, and the backup labels are read back immediately to verify all copies are consistent. If not, you will get a warning of either:

Warning: no backup labels
Warning: some backup labels incorrect

The “format -> backup” command iterate through each of the 5 backup labels and locate the first one that looks good and matchess the geometry (disk type) stored in the backup with the selected disk. If different, something is seriously wrong, and it prompts user if he wants to continue, as an alert the backup is may not be the correct one.  If  a good backup is found, then the values will be  restored, both the primary and backup labels are re-written.


EFI ( Extensible Firmware Interface) Label:

Some quick points about EFI:


  • EFI labels are only supported by 64 bit solaris 9 U 04/03 or later. And able to support the disks larger than 1TB.
  • EFI disks will have total 7 slices ( 0 to 6 usable and slice to as overlap) , similar to SMI disks
  •  ZFS by default used EFI label
  • Size of EFI lable is 34 sectors and In EFI disk no partition can start at sector-0(zero)
  • to initialize a disk with EFI label we should use

format -e  < disk >


Limitations with EFI labeled disks:


  • We can boot from EFI labeled disks.
  • When we move EFI labeled disks to either with older versions of operating systems or older volume manager products ( like VxVM) , operating system will log the errors ” corrupt label – wrong magic number”









I have started unixadminschool.com ( aka gurkulindia.com) in 2009 as my own personal reference blog, and later sometime i have realized that my leanings might be helpful for other unixadmins if I manage my knowledge-base in more user friendly format. And the result is today's' unixadminschool.com. You can connect me at - https://www.linkedin.com/in/unixadminschool/

5 Responses

  1. Yogesh Raheja says:

    Also, in older versions of VXVM we need to label the disks as EFI whenever a new disk is assigned to the OS. I had an experience with this initially when I started playing with vxvm. But now in newer vesrions I guess this limitation has been recovered.

  2. phanishanker@gmail.com says:

    Limitations with EFI labeled disks:

    We can boot from EFI labeled disks.—> Is it we cannot boot from EFI labeled disk

  3. dsanger says:

    You CAN boot from EFI labelled disks on SPARC with the proper firmware: “On SPARC T4 servers, the Sun System Firmware must be at least version 8.4.0. On SPARC
    T5 and SPARC M5 servers, the firmware must be at least version 9.1.0.” See “Managing devices in Oracle Solaris 11.3” p. 94

  1. September 17, 2015

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  2. October 6, 2015

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