On Sun, Jul 26, 2009 at 04:44:45AM +1100, leon zadorin wrote: > Man page for mount_vnd states: > " > The `c' partition of a vnd image should not be used. When a superblock > becomes damaged, fsck_ffs(8) needs information contained in the disklabel > to determine the location of alternate superblocks. This information is > not available when directly using the `c' partition, so checking the file > system image will fail. > " > > Also, the man page for newfs states: > " > Before running newfs or mount_mfs, the disk must be labeled using > disklabel(8). newfs builds a file system on the specified special de- > vice, basing its defaults on the information in the disk label. > " > > But... the man 5 disklabel states: > " > Note that when a disk has no real BSD disklabel the kernel creates a de- > fault label so that the disk can be used. > " > > And indeed, it would appear (or may be my brain is getting sleepy) > that, running newfs on a device (such as svnd0c or vnd0c) which has no > disklabel installed explicitly does work ok... > ... now -- if, as man page for mount_vnd states, fsck_ffs needs > disklabel info when superblock is damaged -- why would it have any > trouble getting the default label that kernel creates for the "disk" > automatically as per man 5 disklabel quote above (the very same info, > I presume that newfs uses when initializing the fs initially on an > image with no explicit label)? > > For example, wrt alternate superblock issues during fskc, the man page > for newfs says: > " > -S sector-size > The size of a sector in bytes (almost never anything but > 512). Changing this is useful only when using newfs to build > a file system whose raw image will eventually be used on a > different type of disk than the one on which it is initially > created (for example on a write-once disk). Note that chang- > ing this from its default will make it impossible for fsck(8) > to find the alternate superblocks if the standard superblock > is lost. > " > > Now, if the default disklabel (created by kernel, on the fly so to > speak) provides info for the sector size (which is used by newfs > during initializing, and by fsck when checking/restoring/fixing, the > fs) then why would it still be bad to use the "c" partition of > svnd/vnd? > > Kind regards > Leon.
'c' is a special partition that the kernel freely changes as the mood hits it. A slight exaggeration. Never use 'c' for anything other than reading/writing raw data. .... Ken
