zfs discuss - Feb 2007 - Which label a ZFS/ZPOOL device has ? VTOC or EFI ?

Hi All,
   
  ZPOOL / ZFS commands writes EFI label on a device if we create ZPOOL/ZFS fs on
it. Is it true ?
   
  I formatted a device with VTOC lable and I created a ZFS file system on it.
   
  Now which label the ZFS device has ? is it old VTOC or EFI ?
   
  After creating the ZFS file system on a VTOC labeled disk, I am seeing the
following warning messages.
   
  Feb  3 07:47:00 scoobyb     Corrupt label; wrong magic number
  Feb  3 07:47:00 scoobyb scsi: [ID 107833 kern.warning] WARNING: /scsi_vhci/ssd
at g600508b400102eb700012000004b0000 (ss
d156):
   
  Any idea on this ?
   
  Your help is appreciated.
   
  Thanks & Regards
  Masthan


 
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Hello dudekula,

Saturday, February 3, 2007, 8:31:24 AM, you wrote:

>

Hi All,

ZPOOL / ZFS commands writes EFI label on a device if we create ZPOOL/ZFS fs on
it. Is it true ?

I formatted a device with VTOC lable and I created a ZFS file system on it.

Now which label the ZFS device has ? is it old VTOC or EFI ?

Depends how you''ve created pool.

If during pool creation you''ve specified entire disk (c0t0d0 - without
slice) then ZFS

put EFI label. Now if you''ve specified slice then ZFS has just used
that slice without

changing anything to label.

You can also check current label with format(1M) utility.

-- 

Best regards,

 Robert                            mailto:rmilkowski@task.gda.pl

                                       http://milek.blogspot.com


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Hi Robert,
   
  Thanks for your quick reply.
   
  As for as my knowledge concerns (because I am new to Solaris) the second slice
(e.g. c0t0d0d2) of disk is exactly same to whole disk (e.g. c0t0d0). It  means
if we create  ZPool on second slice it will create zpool on whole disk.
   
  For example the following two commands does the same job.
   
   
  $zpool create -f mypool c1t0d0
   
  $zpool create -f mypool c1t0d0s2
   
  How the label of the disk differs  from first case ($zpool create -f mypool
c1t0d0) to second case ($zpool create -f mypool c1t0d0s2).
   
   
  Thanks & Regards
  Masthan
   
   
   
   
  

Robert Milkowski <rmilkowski at task.gda.pl> wrote:
          Hello dudekula,
  

  Saturday, February 3, 2007, 8:31:24 AM, you wrote:
  

            >
    Hi All,
   
  ZPOOL / ZFS commands writes EFI label on a device if we create ZPOOL/ZFS fs on
it. Is it true ?
   
  I formatted a device with VTOC lable and I created a ZFS file system on it.
   
  Now which label the ZFS device has ? is it old VTOC or EFI ?
  


  

  

  Depends how you''ve created pool.
  If during pool creation you''ve specified entire disk (c0t0d0 -
without slice) then ZFS
  put EFI label. Now if you''ve specified slice then ZFS has just used
that slice without
  changing anything to label.
  

  You can also check current label with format(1M) utility.
  

  

  

  

  -- 
  Best regards,
   Robert                            mailto:rmilkowski at task.gda.pl
                                         http://milek.blogspot.com


 
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On 04 February, 2007 - dudekula mastan sent me these 7,5K bytes:
> Hi Robert,
>    
>   Thanks for your quick reply.
>    
>   As for as my knowledge concerns (because I am new to Solaris) the
>   second slice (e.g. c0t0d0d2) of disk is exactly same to whole disk
>   (e.g. c0t0d0).
Almost, but no.
>   It  means if we create  ZPool on second slice it will
>   create zpool on whole disk.
>    
>   For example the following two commands does the same job.
>    
>    
>   $zpool create -f mypool c1t0d0
>    
>   $zpool create -f mypool c1t0d0s2
>    
>   How the label of the disk differs  from first case ($zpool create -f
>   mypool c1t0d0) to second case ($zpool create -f mypool c1t0d0s2).
If the disk has VTOC label, there is no "c1t0d0".. ZFS will see that
you''re "kinda" referring to the whole disk and change it into
EFI.
With the second version, you''re using a slice (that just happen to
cover
all of the disk) and it won''t change to EFI and won''t mess
around with
the write cache for additional performance.

/Tomas
-- 
Tomas ?gren, stric at acc.umu.se, http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Ume?
`- Sysadmin at {cs,acc}.umu.se

On Feb 3, 2007, at 02:31, dudekula mastan wrote:
> After creating the ZFS file system on a VTOC labeled disk, I am  
> seeing the following warning messages.
>
> Feb  3 07:47:00 scoobyb     Corrupt label; wrong magic number
> Feb  3 07:47:00 scoobyb scsi: [ID 107833 kern.warning] WARNING: / 
> scsi_vhci/ssd at g600508b400102eb700012000004b0000 (ssd156):
>
> Any idea on this ?
This generally means that this device doesn''t have a label - and this  
particular device would be the multipathed device identified by the  
GUID 600508b400102eb700012000004b0000 or the old BSD style driver  
enumeration ssd156 .. (take a look at http://access1.sun.com/ 
codesamples/disknames.html to see an example on how to use libdevinfo  
to convert this to the SVR4 c#t#d# style name)

Now with ZFS if you don''t specify a slice, you''re essentially
asking
ZFS to use and autolabel the entire disk which will put an EFI style  
label on since the older sun style VTOC labels have an upper limit of  
1TB per disk (EFI should work up to 2^64 LBAs.)  The older sun VTOC  
labels typically use slice 2 as a backup to show the entire disk and  
will store the label in the first 512B, whereas the EFI labels will  
use 34 sectors at the start of the disk to store the label, and will  
also reserve a portion at the tail end of the disk for a backup label.

With the older sun style VTOC labels, if you ever overwrite the first  
the first 512B on cylinder 0 of the disk (eg: dd if=/dev/zero of=/dev/ 
rdsk/c1t1d0s2 where s2 is the typical backup label starting at  
cylinder 0) you''ll overwrite the label, whereas with the EFI label  
you have to overwrite both protected sections of the disk.

So to reiterate what Robert and Tomas have already gone into .. if  
you plan on using the entire disk and want the vdev benefits (the  
ability to import/export pools, write caching, etc) you should  
probably not specify a slice and allow ZFS to autolabel the disk as  
it sees fit.

hth
----
.je
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