kern/164741: zvol always present as 512 bytes/sector regardless of blocksize

[Pete French]

>Number:         164741
>Category:       kern
>Synopsis:       zvol always present as 512 bytes/sector regardless of blocksize
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Feb 03 16:50:09 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Pete French
>Release:        FreeBSD 8.2-STABLE amd64
>Organization:
Ingresso Ltd
>Environment:
System: FreeBSD dilbert.london-internal.ingresso.co.uk 8.2-STABLE FreeBSD 8.2-STABLE #0: Fri Jan 6 12:44:04 GMT 2012 petefrench at dilbert.london-internal.ingresso.co.uk:/usr/obj/usr/src/sys/GENERIC amd64


	
>Description:

	A zvol may be created with a specific sectorsize, specified with -b
	or the volblocksize property. The resulting device in /dev/zvol
	always appears to have 512 bytes per sector however, as reported by
	diskinfo

>How-To-Repeat:

        # zfs create -V 1G -b 512 tank/test1
        # zfs create -V 1G -b 4k tank/test2
        # zfs create -V 1G tank/test3
        # zfs get volblocksize tank/test1 tank/test2 tank/test3
        NAME        PROPERTY      VALUE     SOURCE
        tank/test1  volblocksize  512       -
        tank/test2  volblocksize  4K        -
        tank/test3  volblocksize  8K        -
        # diskinfo /dev/zvol/tank/test*
        /dev/zvol/tank/test1    512     1073741824      2097152 0       0
        /dev/zvol/tank/test2    512     1073741824      2097152 0       0
        /dev/zvol/tank/test3    512     1073741824      2097152 0       0

>Fix:

	For zvols to be uses as iscsi devices the desired blocksize can
	be specified in the istgt config file. For volumes being used
	internally however (e.g. as volumed for VirtualBox machines)
	I have discovered no workaround.

>Release-Note:
>Audit-Trail:
>Unformatted: