From: nathan@laplace.biology.yale.edu (Nathan F. Janette)
Subject: NeXT-FAQ.disks: Questions about disk drives
Reply-To: nathan@laplace.biology.yale.edu
Organization: Yale University, Department of Computer Science, New Haven, CT
Date: Thu, 23 Jul 1992 21:46:08 GMT
Expires: Fri, 28 Aug 1992 00:00:00 GMT

NeXT-FAQ.disks: Questions about disk drives


*** Subject: D1. What disk drives will work with the NeXT?

First get a copy of NextAnswers and review hardware.586

Most scsi disk drives will work with 2.0 without
modifying disktab. You should read the Network and
Systems Administrator manual provided with all new
systems and available on-line on 2.0 extended.  There
have been problems with the installation of boot blocks
and badly formed  fstab generated by BuildDisk.  A disk
connected to the NeXT will need to have a NeXT specific
label written to it before it can be properly recognized
by the system.  If you get an error message "Invalid
Label..." this indicates that the drive was
successfully seen by the NeXT machine but it does not have
the proper label, to install a label use the
/usr/etc/disk program on the raw disk device that the
system assigned to the device and use the label command to
write the label onto the disk. [how the NeXT assigns disk
devices is explained in the N&SA manual]

NeXT provides a low level disk formatter with 2.0, most
drives are already formatted at the factory.  The sdform
program does not offer much flexibility.

[If someone is keeping a list of drives that work with the
NeXT we would like to know about it (send mail to
next-faq@media.mit.edu). This type of list would be
useful to keep on sonata.cc.purdue.edu in the
pub/next/FAQ directory.  Also there was talk about Mac
drives *not* working on the NeXT due to their
implementation of the SCSI standard.] 


*** Subject: D2. How do I customize BuildDisk to create a bootable disk of my  
own configuration?

The BuildDisk application is extremely limited in terms
of the  types of disks configuration it knows how to build. 
Essentially it "knows" about swapdisks, optical disks,
330 and 660 MB SCSI disks. If you wish to do custom
configurations you should look at existing BLD script
files in /etc/BLD.*  There is a script which you can use to
specify which BLD script you are using, which disktab
entry, and other useful parameters in
/usr/etc/builddisk 

Some things to note: - the fstab installed on the target
disk is specified in the newclient command in the BLD
script.  standard fstabs are extracted from
/usr/template/client/fstab.* - the BLD scripts do not
put down a new boot block on the scsi disk, you may want to
install one by hand using the /usr/etc/disk program. -
some disks boot fine but NeXTstep comes up with a blank
window and no login window.  This is due sometimes to
forgetting to install an accessible
/NextLibrary/{Fonts,Sounds}  In general you need quite
a lot of things to make a bootable disk. 

Mike Carlton adds - you can build a minimally usable
bootable floppy (for crash recovery purposes).  There is
a modified version of builddisk (to make it support
building floppies, a minimal change) and a BLD script to
build the boot floppy available at cs.orst.edu in
next/sources/Bootfloppy.tar.Z.  (I put this together
in response to several requests.)  A newer version of
Bootfloppy for 2.1 is on the archives as
next/sources/util/Bootfloppy2.1.tar.Z 


*** Subject: D3. How much disk space is lost due to formatting and file system  
overhead?

Rex Pruess (rpruess@umaxc.weeg.uiowa.edu) offers the
following explanation: Let's assume you bought a disk
drive advertised with 400 MB unformatted capacity. 
Vendors are not consistent with the MB definition.  You
may have much less space less than you think you have. 
Which of the following did you buy? 

         400 * 1000 * 1000 = 400,000,000 bytes
         400 * 1024 * 1000 = 409,600,000 bytes
         400 * 1024 * 1024 = 419,430,400 bytes

The disk must be formatted.  This is often done by the
vendor, but occasionally by the user.  Formatting maps
the disk into sectors.  Space is reserved for the disk
geometry and bad sectors.  Formatting can take 10-20% of
the capacity depending on the sector size.  Common sector
sizes are 512 and 1024.  Generally, bigger sectors mean
less waste.

Once formatted, the UNIX file system must be created.  On
the NeXT, this is one of the steps performed by the
BuildDisk application.  It invokes the mkfs command to
make a file system.  This reserves space for the UNIX file
system (e.g., superblocks, inode tables).  This
overhead can take another 2-3% of the available disk
space.

If you issue the df command, you may be surprised to see
another 10% the available disk space has disappeared. 
The df command shows the total, used, and available disk
space.  The df units are in kbytes (1024 bytes). The sum of
the used and available numbers will generally be about
10% less than the total kbytes.  This space is reserved to
allow the UNIX file system to be efficient in its storage
allocation.  If your disk fills up, only the superuser can
store files in the remaining 10%. 

To complete the picture, here's a snapshot of what may occur:

	 Capacity     Lost/Used/Reserved    Reason
	(in bytes)       (in bytes)
        419,430,000      19,430,000         Marketing hype (~5%)
	400,000,000      60,000,000         Formatting (~15%)
	340,000,000       6,800,000         UNIX file system (~2%)
	333,200,000      33,320,000         Efficiency & superuser (~10%)
	299,880,000          -                 -

For more information, refer to the df and mkfs man pages.


*** Subject: D4. Can I run my SCSI-2 disks in synchronous mode?

Quick answer is: No!  Reason is that the NeXT does not
support synchronous transfers from the SCSI bus.  It does
support SCSI-2 disks running in asynchronous mode,
which all SCSI-2 disks must do. 


*** Subject: D5. How do I configure my HP 660 to boot properly?

It has been reported that HP drives fail to autoboot on
power on or while other devices are on the scsi bus.  The
problem seems to be with drives configured to spin-up
automatically on power on do not get recognized at boot
time.  To remedy this problem reliably with HP 660Mb
(HP97548) and 1Gbyte (HP 97549) drives remove the auto
spinup jumper on the back of the drive.  Looking at the disk
from the back with the power connector on the lower left,
it is the sixth jumper. 


*** Subject: D6. What is the procedure for installing a Fujitsu M2263SA/SB SCSI  
Disk as the NeXT Boot Disk?

See Izumi Ohzawa's note in
/pub/next/docs/fujitsu.recipe available via
anonymous ftp from sonata.cc.purdue.edu. 



--
Editor:
Nathan Janette nathan@laplace.csb.yale.edu


--
Nathan Janette		"I'm a NeXTstep man,
Dept MB&B, Yale Univ	 I'm a NeXTcube guy"
New Haven, CT
nathan@laplace.biology.yale.edu (NeXT)

Newsgroups: comp.sys.next.announce