[4868] in linux-scsi channel archive
Re: 2K sectors
daemon@ATHENA.MIT.EDU (Eric Youngdale)
Tue Oct 13 06:41:24 1998
Date: Mon, 12 Oct 1998 22:24:24 -0400 (EDT)
From: Eric Youngdale <eric@andante.jic.com>
To: William Brioschi <capo@writeme.com>
cc: Linux SCSI mailing list <linux-scsi@vger.rutgers.edu>
In-Reply-To: <m0zRBHG-00022yC@fire.casa.brioschi.net>
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.
>
> I think there are three possibilities to be able to access a cartdridge:
> 1) make Linux scsi disk and low level drivers digest the big sectors; this is
> probably not a very good idea, unless it's already been done in a newer
> kernel... has it?
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
have no way of verifying it myself (I could contrive a way to test it if
need be).
That being said, it is more than the disk driver that needs to
grok the larger blocksize. Each filesystem needs to be able to tolerate
it as well. Finally, the filesystem itself needs to be created with a
blocksize >= the hardware sectorsize.
The reactions that I have gotten from people are that for
something like ext2, it works fine. With the msdos filesystem (in some
flavor or another) it doesn't - I passed this comment along to the person
who was maintaining that code in the hope that we find the problem.
> 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?
> 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.
-Eric
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