Path: utzoo!utgpu!cunews!bnrgate!brtph3!brchh104!brchs1!bnr.ca!rice.edu!sun-spots-request
From: pln@egret1.stanford.edu (Patrick L. Nolan)
Newsgroups: comp.sys.sun
Subject: Large disks hazardous to your data?
Keywords: Hardware
Message-ID: <1990@brchh104.bnr.ca>
Date: 19 Mar 91 18:33:00 GMT
Sender: news@brchh104.bnr.ca
Organization: Sun-Spots
Lines: 31
Approved: Sun-Spots@rice.edu
X-Original-Date: 8 Mar 91 17:41:43 GMT
X-Sun-Spots-Digest: Volume 10, Issue 56, message 17
X-Note: Submissions: sun-spots@rice.edu, Admin: sun-spots-request@rice.edu

The March 4 issue of Digital News has an article with the headline "User
data at risk with 1.2 GB disks."  Here are some excerpts from the article:

  Customers configuring ... SCSI hard disk drives of more than 1 GB run
  a serious risk of losing their stored data.

  The SCSI implementation found in Ultrix and all VMS operating
  systems except version 5.4 is unable to address hard disk drives
  larger than 1 Gbyte, meaning that users with disks formatted at 
  more than 1 Gbyte are paying for storage space they cannot possibly
  access.  And, in attempting to do so, they could lose all their data.

  The problem ... does not occur when using a later version of the
  SCSI I/O driver, called Extended SCSI.

  According to SCSI specialists, the SCSI Group 0 set of commands,
  which are also embedded into some Sun Microsystems ... operating
  systems, can address a maximum of 1.073742 GBytes.  On disks
  with a larger formatted capacity, the SCSI I/O driver wraps
  around the disk and overwrites the first block of data, called
  the superblock or home block, thereby preventing access to the rest of
  the data on the disk....

  "The Group 0 commands are a relatively primitive SCSI I/O driver;
  they only allocate 6 bytes for addressing and don't offer
  diagnostics ... Most of the new SCSI implementations use the
  Group 1 or Extended SCSI commands."

This is pretty alarming.  I think it would be of general interest if some
experts on the Sun SCSI implementation could tell us whether we have Group
0 or Group 1.  Are they implemented in hardware or software?