Reading random disk blocks with format

Occasionally it is useful to be able to read blocks from disks when there is no label on the disk. Since most applications won't be able to open the device as you need to use O_NDELAY flag to the open system call.

Luckily it is possible to use format to read arbitrary disk blocks so you don't have to resort to writing a special application. The trick is to use the read analysis option to format and then restrict the blocks that you want to read down to the the blocks that you are interested in. Then once read use the print buffer command to output the data:

# format

Searching for disks...done


AVAILABLE DISK SELECTIONS:
       0. c0t0d0 <SUN9.0G cyl 4924 alt 2 hd 27 sec 133>
          /pci@1f,4000/scsi@3/sd@0,0
Specify disk (enter its number): 0
selecting c0t0d0
[disk formatted]
Warning: Current Disk has mounted partitions.


FORMAT MENU:
        disk       - select a disk
        type       - select (define) a disk type
        partition  - select (define) a partition table
        current    - describe the current disk
        format     - format and analyze the disk
        repair     - repair a defective sector
        label      - write label to the disk
        analyze    - surface analysis
        defect     - defect list management
        backup     - search for backup labels
        verify     - read and display labels
        save       - save new disk/partition definitions
        inquiry    - show vendor, product and revision
        volname    - set 8-character volume name
        !<cmd>     - execute <cmd>, then return
        quit
format> ana


ANALYZE MENU:
        read     - read only test   (doesn't harm SunOS)
        refresh  - read then write  (doesn't harm data)
        test     - pattern testing  (doesn't harm data)
        write    - write then read      (corrupts data)
        compare  - write, read, compare (corrupts data)
        purge    - write, read, write   (corrupts data)
        verify   - write entire disk, then verify (corrupts data)
        print    - display data buffer
        setup    - set analysis parameters
        config   - show analysis parameters
        !<cmd>   - execute <cmd> , then return
        quit
analyze> set
Analyze entire disk[yes]? no
Enter starting block number[0, 0/0/0]: 0
Enter ending block number[0, 0/0/0]: 0
Loop continuously[no]? 
Enter number of passes[2]: 1
Repair defective blocks[yes]? 
Stop after first error[no]? yes
Use random bit patterns[no]? 
Enter number of blocks per transfer[1, 0/0/1]: 
Verify media after formatting[yes]? 
Enable extended messages[no]? 
Restore defect list[yes]? 
Restore disk label[yes]? 

analyze> read
Ready to analyze (won't harm SunOS). This takes a long time, 
but is interruptable with CTRL-C. Continue? y

        pass 0
   0/0/0  

Total of 0 defective blocks repaired.
analyze> print
0x53554e39  0x2e304720  0x63796c20  0x34393234  0x20616c74  0x20322068  
0x64203237  0x20736563  0x20313333  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000001  0x00000000  0x00000000  0x00080002  
0x00000003  0x00010005  0x00000000  0x00010000  0x00010000  0x00010000  
0x00010000  0x00010000  0x00000000  0x00000000  0x00000000  0x600ddeee  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x1518133e  0x00000000  0x00000001  
0x133c0002  0x001b0085  0x00000000  0x00000000  0x00fdc0a1  0x00001217  
0x00100e03  0x00000000  0x010dcea4  0x00000000  0x00000000  0x00000000  
0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  0x00000000  
0x00000000  0xdabe5344  
analyze> 


Now I know those at the back will recongise this as a Solaris SPARC disk label. With vtoc, that give away VTOC_SANITY values of 0x600ddee being in the middle after the ASCII label

Comments:

Holy smokes, I got nostalgia reading this...

But, wouldn't it have been easier to just use:

dd if=/dev/rdsk/c#t#d#s2 of=/var/tmp/c#t#d#s2.dump bs=1024 count=1

And then use a hex editor, or even a small AWK script to decode the dump?

Speaking of which, do you know of any good hex editors on Solaris?

Posted by UX-admin on December 23, 2008 at 11:37 AM GMT #

Well dd would be good but if the disk has no label you can't open it without using O_NDELAY and dd does not. An RFE that needs logging.

As to a hex editor, ghex is not terrible even if I would like it to include a disassembler as well.

Posted by Chris Gerhard on December 23, 2008 at 03:03 PM GMT #

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This is the old blog of Chris Gerhard. It has mostly moved to http://chrisgerhard.wordpress.com

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