From: Jonathan Williams (jonathw@shubertorg.com)
Date: Thu Nov 07 2002 - 15:39:57 EST
Wow...that was fast.
I received a couple of emails already, and don't feel I need any more to answer
the question.
----------------------
The first response I got was my fave:
> Should I be worried?
Nope.
Elizabeth Harvey-Forsythe
MIT Media Lab
----------------------
And then the good Doctor spoke with a bit more clarification:
>From Dr. Thomas Blinn:
You have two separate "things" between your Informix database and the
real raw physical disks: LSM and the HSG80. Both of these prevent
Informix from ever accessing the "real" disk directly. LSM presents
to Informix an abstracted "volume" which looks enough like a raw disk
for Informix to use it (I am assuming you have Informix talking to
the "raw" volumes, not through, say, an AdvFS file system interface),
and below LSM, the HSG80 is probably also presenting an abstracted
volume (unless you configured all the disks as "JBOD" which clearly
you didn't do if you've got hardware mirroring turned on). So by the
time Informix can access things, there are other things preventing it
from over-writing any disk label.
I suspect you can ask the UNIX "disklabel" utility to read the disk
label on the HSG80 volumes, but all you'll see is the LSM "metadata",
not a typical UNIX disk label for a "raw" disk. And unless you make
changes in the way the HSG80 "exports" the volumes to make it give
you JBOD access to the raw disk drives, you can't really get to the
raw disks themselves.
The bottom line: don't worry about it.
------------------
Well, that's enough for me.
Thanks everyone for all the other replys as well. =)
Jonathan Williams
Unix Systems Administrator
The Shubert Organization, Inc.
----- Original Message -----
From: "Jonathan Williams" <jonathw@shubertorg.com>
To: "Tru64-Unix-Managers@Ornl. Gov (E-mail)" <tru64-unix-managers@ornl.gov>
Sent: Thursday, November 07, 2002 3:12 PM
Subject: 72GB Ultra3 SCSI question
> We have a storageworks cabinet with a bunch of those 72.8GB 10K RPM Ultra3
SCSI
> disks (part No. 232432-B22). We use these disks for Informix Databases. My
DBA
> over here just gave me this document talking about allocating disk space for
the
> database (nice document to read after you've been online with it for a year
and
> a half). He just wants to make sure the way we set up these disks was
> correct...or if we've just been extremely lucky for the past 18 months with
this
> system. This is what the document said:
>
> "Many computer systems and some disk-drive manufacturers keep information for
a
> physical disk drive on the drive itself. This information is sometimes
referred
> to as a valume table of contents (VTOC) or disk label. The VTOC is commonly
> stored on the first track of the drive. A table of alternate sectors and
> bad-sector mappings (also called a revectoring table) might also be stored on
> the first track.
> If you plan to allocate partitions at the start of a disk, you might need to
> use offsets to prevent the databse server from overwriting critical
information
> required by the operating system. For the exact offset required, refer to
your
> disk-drive manuals"
>
> Well that would be nice, but I don't have any manuals for the disk drives, and
> couldn't seem to locate much info at all about these drives through various
> google searches (but I did see some places with some pretty good prices).
>
> Anyway...I was just wondering if these disks, or if the operating system
(Tru64
> 5.1, and 5.1a) requires an offset so that you don't overwrite the disk labels.
> The disks are in a storageworks cabinet with HSG80 controllers that go to a
> 16-port fibre switch, which goes to the system. The disks are hardware
mirrored
> through the controllers. Operating system wise, the disks are sliced up with
> LSM. No offsets were used on the first volume, so the data does begin at the
> beginning of the disks.
> I don't think I'm overwriting the disk labels on these drives, I'm sure I
would
> have noticed pretty quickly .
>
> But can anyone give me some more info on this? Should I be worried?
>
>
> Jonathan Williams
> Unix Systems Administrator
> The Shubert Organization, Inc.
>
>
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