zfs discuss - Sep 2008 - zpool error: must be a block device or regular file

Hey folks,

Can anybody help me out with this.  I''ve finally gotten my hands on a
Micro Memory nvram card, but I''m struggling to get it working with ZFS.
The drivers appeared to install fine, and it works with ZFS if I use the
/dev/dsk device, but whenever I try to use rdsk I get the error:

# zpool create test /dev/rdsk/c3d1p0
cannot use ''/dev/rdsk/c3d1p0'': must be a block device or
regular file

Unfortunately I''m once again at the limits of my Solaris knowledge, so
any help you folks can give will be very much appreciated.

thanks,

Ross
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This message posted from opensolaris.org

/dev/rdsk/* devices are character based devices, not block based.  In general,
character based devices have to be accessed serially (and don''t do
buffering), versus block devices which buffer and allow random access to the
data. If you use:
ls -lL /dev/*dsk/c3d1p0
you should see that the /dev/dsk/c3d1p0 device is a block based device and
/dev/rdsk/c3d1p0 (via the first letter of the ''ls'' output).

So while /dev/rdsk/xxx and /dev/dsk/xxx point to the same hardware, the access
methods that are available via the two interfaces are very different.
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This message posted from opensolaris.org

Oh, ok.  So /dev/rdsk is never going to work then.  Mind if I pick your brain a
little more then while I try to understand this properly.

The man pages for the nvram card state that /dev/rdsk will normally be the
preferred way to access these devices, since /dev/dsk is cached by the kernel,
which negates some of the benefits of having nvram based storage.

Is that something I should be concerned about when using one of these as a slog
device?  Or will ZFS be flushing data from the kernel cache to the disk often
enough that it''s not a problem?
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This message posted from opensolaris.org

The zfs kernel modules handle the caching/flushing of data across all the
devices in the zpools.  It uses a different method for this than the
"standard" virtual memory system used by traditional file systems like
UFS.  Try defining your NVRAM card with ZFS as a log device using the
/dev/dsk/xyz path and let us know how it goes.
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This message posted from opensolaris.org