[4872] in linux-scsi channel archive
Re: 2K sectors
daemon@ATHENA.MIT.EDU (Dr. Michael Weller)
Tue Oct 13 13:40:34 1998
Date: Tue, 13 Oct 1998 13:23:11 +0200 (MESZ)
From: "Dr. Michael Weller" <eowmob@exp-math.uni-essen.de>
To: William Brioschi <capo@writeme.com>
Cc: Linux SCSI mailing list <linux-scsi@vger.rutgers.edu>
In-Reply-To: <Pine.LNX.3.96.981012222042.9681A-100000@andante.jic.com>
On Mon, 12 Oct 1998, Eric Youngdale wrote:
>
> On Thu, 8 Oct 1998, William Brioschi wrote:
>
> > I have a 640M magneto-optical drive which uses 2K blocks.
> > Of course, Linux (2.0.29) complains about the unsupported sector size.
> >
> > I _have_ to use it, mainly for backup purposes. Performance is not an issue:
> > I would be happy with a 100K/sec.
> In the 2.1 series kernel, the disk and low-level drivers should
> already (in theory) handle this case. I don't have such a disk, so I
There were patches for older kernels doin a similar thing around, yet they
were not perfect (hence not put in 2.0 mainstream kernels)
[...]
> > 2) make the drive understand I need 1K sectors; the SCSI-HOWTO says something
> > about the MODE SELECT command, how can I send it? will it work? will I have
> > to reformat the cartdridges (which come preformatted at low level with a 2K
> > sector)? how will I lo level format a cartdridge?
All this can be done IN THEORY, with scsiinfo package. Alas, the device
must accept it. You'll almost certainly have to reformat too. In your
situation, all I heard about these 640MB MO's, the hardware simply does
not support it. (IMHO: MOs are hard sectored anyway).
> > 3) use the device in raw, sequential mode (through tar or something like that),
> > probably using the SCSI generic driver; I haven't tried this yet, is it
> > possible? should I do something particular or can I simply do a
> > "tar cf /dev/sga"?
>
> This absolutely won't work. The generics driver simply doesn't
> work like this.
Yep, a plain "tar cf /dev/sga" does not work. Linux does not have the
raw(char device) and block device combos used to access disks on other
unixes circumventing the buffer cache (but as a disk is never a char
device, the raw devices are no real char devices anyway). In theory it
would help here, if there were a non buffer sequential /dev/sda with
linux, alas there is not. Like Eric said, /dev/sga is not just a raw
/dev/sda. It is a simple means to pass raw scsi command to the disk.
Hence, this does not mean some can code a user level app 'wdisk' to do:
tar cf - | wdisk /dev/sga . But is it worth the effort?
Just my additional 2 pence,
Michael
--
Michael Weller: eowmob@exp-math.uni-essen.de, eowmob@ms.exp-math.uni-essen.de,
or even mat42b@spi.power.uni-essen.de. If you encounter an eowmob account on
any machine in the net, it's very likely it's me.
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