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Full Discussion: Does formatting slice 2 (backup) destroy disk geometry?
Top Forums UNIX for Dummies Questions & Answers Does formatting slice 2 (backup) destroy disk geometry? Post 302561656 by mia-chan on Tuesday 4th of October 2011 09:11:30 PM
Old 10-04-2011
Question Does formatting slice 2 (backup) destroy disk geometry?
I am a new Unix Sys Admin who is learning mostly from books with minimal classroom training (ie: no certificates, training is largely hands-on, conducted at work). I work with Solaris 8 through 10, and with some fairly outdated hardware. In my work restoring old workstations I have been instructed to avoid formatting or "newfs-ing" slice 2 (which is reserved for "backup" in our systems, marked with flag "wu"); I am told this will destroy the "disk architecture" or "disk geometry" and render it unusable. Despite the warning, I have made the error of formatting slice 2 (using the "format" command), and while the partition spans the entire disk (per our partition tables), I was informed that I have destroyed the disk in the process. To make matters worse, I built a file system on slice 2 with "newfs."

I have done lengthy research online trying to determine exactly what disk geometry or disk architecture is and how it is possible that software can destroy a physical disk but I am at a loss. I understand that slice 2 is historically "reserved" and spans the entire disk; what I do not understand is how altering this slice can destroy a disk.

Can anyone shed any light on this argument? Or better yet, can anyone tell me how to test this theory or recover from the damage I have caused? Is this just an antiquated idea with "historical" significance only or have I really and truly destroyed a piece of hardware with a simple command?

Thanks in advance!
 

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LEARN ABOUT OPENSOLARIS

cmdk

cmdk(7D)							      Devices								  cmdk(7D)

NAME

       cmdk - common disk driver

SYNOPSIS

       cmdk@target, lun : [ partition | slice ]

DESCRIPTION

       The  cmdk  device  driver  is  a  common interface to various disk devices. The driver supports magnetic fixed disks and magnetic removable
       disks.

       The cmdk device driver supports three different disk labels: fdisk partition table, Solaris x86 VTOC and EFI/GPT.

       The block-files access the disk using the system's normal buffering mechanism and are read and written  without	regard	to  physical  disk
       records. There is also a "raw" interface that provides for direct transmission between the disk and the user's read or write buffer. A sin-
       gle read or write call usually results in one I/O operation; raw I/O is therefore considerably more efficient when many bytes are transmit-
       ted. The names of the block files are found in /dev/dsk. Raw file names are found in /dev/rdsk.

       I/O  requests  to the magnetic disk must have an offset and transfer length that is a multiple of 512 bytes or the driver returns an EINVAL
       error.

       Slice 0 is normally used for the root file system on a disk, slice 1 as a paging area (for example, swap), and slice 2 for backing  up  the
       entire fdisk partition for Solaris software. Other slices may be used for usr file systems or system reserved area.

       The fdisk partition 0 is to access the entire disk and is generally used by the fdisk(1M) program.

FILES

       /dev/dsk/cndn[s|p]n	 block device (IDE)

       /dev/rdsk/cndn[s|p]n	 raw device (IDE)

				 where:

				 cn    controller n.

				 dn    lun n (0-1).

				 sn    UNIX system slice n (0-15).

				 pn    fdisk partition (0-36).

       /kernel/drv/cmdk 	 32-bit kernel module.

       /kernel/drv/amd64/cmdk	 64-bit kernel module.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Architecture		     |x86			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fdisk(1M), mount(1M), lseek(2), read(2), write(2), readdir(3C), scsi(4), vfstab(4), attributes(5), dkio(7I)

SunOS 5.11							    4 Nov 2008								  cmdk(7D)
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