Re: [gentoo-user] Re: mount: "special device /dev/hdc does not exist". What does this mean?

[Alan Mackenzie]

Hi, Nikos!

On Sun, Jul 20, 2008 at 12:29:19AM +0300, Nikos Chantziaras wrote:
> Alan Mackenzie wrote:
> >>The default in new kernels is to only use /dev/sd*.

> >I'm totally confused.  Doesn't "sd*" mean "SCSI disk drive"?  When I was
> >installing Gentoo from the CD, I had to mount my main hard drive as
> >/dev/sdb5.  When I built my own kernel, it needed /dev/hdh5.

> >This seems crazy.  Is it documented anywhere in Gentoo?

> Not sure.  But if you have /dev/hd* instead of /dev/sd*, it means you
> configured your kernel with the legacy IDE drivers instead of the new
> (P)ATA drivers.  The new drivers use /dev/sd* (for IDE/PATA/SATA and
> SCSI alike; there's no difference anymore.)

This was indeed the case.

> The CD/DVD-ROM can show up as /dev/sd* even with the old legacy drivers
> if you have enable "SCSI Emulation" for it.

> In any event, try to build a new kernel using the new drivers.  The old
> legacy driver you're using will probably get declared "deprecated" at
> some point (if it didn't happen already).

[ Detailed instructions snipped - but they were appreciated and followed
:-]

Did this.  It mapped my two hard drives (previously /dev/hd[gh]) to
/dev/sd[ab], and created /dev/sda, dev/sda1, .....  So far, so good.

However, it hadn't created /dev/sda16 or /dev/sda17 for some reason.  A
quick # ls -l /dev/sd{a15,b} gives:

... 8, 15  /dev/sda15
... 8, 16  /dev/sdb

In a philosophical mood, one might say that the new "unified",
"enhanced", "better" IDE support is inadequate for my setup.  What I
actually said, I'm not going to repeat in a public mailing list.

So the kernel guys have decided that nobody would ever want more than 15
partitions on a drive.  It's a bit like the old MS-DOS restriction to 512
MB all over again.  Hey, guys, hard drives nowadays are like 200 gig, not
512meg.  What's so wrong about having partitions with sizes 1Gb, 2Gb, 4Gb,
with maybe 100Mb for a boot partition?

>    < >   Generic ATA support

> unless you can't find a native driver for your chipset (I doubt you have
> some extremely rare/exotic mainboard ;)

The HPT370A UDMA100 chip (with my two hard drives) was no problem.  For
the VIA VT82C586A/B/VT82C686/A/B/VT823x/A/C "ordinary" IDE chip (the one
with my two DVD drives attached), I tried configuring "VIA", which
didn't work.  Then I rebuilt the kernel again with "Generic ATA
support", which didn't work either.

Both of these created /dev/sdc and /dev/sdc1, but no /dev/sdd.  When I
tried # mount -t iso9660 /dev/sdc /cdrom, I got the "something's gone
wrong, but we're not telling you what" error message.  Trying to mount
/dev/sdc1 gave exactly the same result.  Actually, thinking about it,
this was probably my USB stick it was trying to access.

Nikos, do you happen to know the appropriate kernel mailing list where I
could express the opinion that restricting the number of partitions on a
drive to 15 isn't a good tradeoff?

All in all, I really amn't impressed with this "modern" drive support.
Besides quartering the max number of partitions on a drive, it confuses
IDE and SCSI drives, thus confusing me, too.  Previously, when I
attached devices to the IDE1 socket, I knew they would appear at
/dev/hd[cd].  Now, it would seem, the kernel assigns drives at random to
/dev/sd[abcd...], so you can only determine by experiment which devices
are at which "device".  Nothing personal, Nikos.  ;-)

I think I need to go back to the traditional IDE handling.

None of the Gentoo kernels I've built have even seen my two DVD drives,
yet.  I'll get there, somehow.

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).