Should I use offset on first disk partitions ???

[Paulo Amorim]

Hello

Many people say that we must use offset when creating a dbspace/chunk
located on the first partition of a physical disk, due to problems that
may occur with the disk identification area (magic number). This number
could be overwrited, and then the disk could be lost.

What is the true in all this ??

I had this problem on a Sun machine about 2 years ago. We defined a raw
device with the same size of the disk (2Gb) and created a dbspace with
the same size, and every time the system was rebooted, the dbspace was
lost. The problem was solved by defining a small partition of disk just
to the magic number, and the rest of the disk to the raw device. Some
time after this, Informix Techinical Support told me that we must
always use offset when creating the rootdbspace, and without this we
certainly would have this problem.

I´ve seen many other Sun machines, and many other machines, and I never
saw any problems like this again, and I never saw anybody using this
rule. In many machines, the dbspaces were defined with the same size of
the raw devices, and the raw devices were defined with the same size of
the disks.

Now I had the same problem with another Sun machine, but this time with
a disk array, and with a chunk that was not the rootdbs, and the Sun
diagnostic was that I should have created the dbspace with offset.

On Informix release notes there is nothing about this in any plattaform.

Does anybody have an opinion about this ???

Thanks !!!

--
Paulo Roberto Marelli de Amorim
TS&0 Consulting
Brasil

Sent via Deja.com http://www.deja.com/
Before you buy.

[Neil Truby]

Some OSs use the first portion of a disk for its vtoc. Solaris is one.
HP-UX definitely doesn't do this, nor does NCR's variant. I can't comment
on any others.

So, in Solaris, if you're to use the first slice of a disk for an Informix
raw device, either start the slice from cylinder 1 rather than 0 in format,
or provide a 4k offset with onspaces/onmonitor. It's immaterial what type
of dbspace you will create in the slice (rootdbs etc.). In fact, this isn't
just a problem for Informix, but for Sybase too, and presumably for any
other DBMS that uses raw devices.

Neil Truby
Londis Stores
Hampton Hill, UK

Paulo Amorim wrote in message <81lvbj$90e$1...@nnrp1.deja.com>...

>Hello
>
>Many people say that we must use offset when creating a dbspace/chunk
>located on the first partition of a physical disk, due to problems that
>may occur with the disk identification area (magic number). This number
>could be overwrited, and then the disk could be lost.
>
>What is the true in all this ??
>
>I had this problem on a Sun machine about 2 years ago. We defined a raw
>device with the same size of the disk (2Gb) and created a dbspace with
>the same size, and every time the system was rebooted, the dbspace was
>lost. The problem was solved by defining a small partition of disk just
>to the magic number, and the rest of the disk to the raw device. Some
>time after this, Informix Techinical Support told me that we must
>always use offset when creating the rootdbspace, and without this we
>certainly would have this problem.
>

>I扉e seen many other Sun machines, and many other machines, and I never

[David Williams]

In article <81o890$h49$1...@taliesin.netcom.net.uk>, Neil Truby
<ntr...@netcomuk.co.uk> writes

>Some OSs use the first portion of a disk for its vtoc. Solaris is one.
>HP-UX definitely doesn't do this, nor does NCR's variant. I can't comment
>on any others.
>
>So, in Solaris, if you're to use the first slice of a disk for an Informix
>raw device, either start the slice from cylinder 1 rather than 0 in format,
>or provide a 4k offset with onspaces/onmonitor. It's immaterial what type
>of dbspace you will create in the slice (rootdbs etc.). In fact, this isn't
>just a problem for Informix, but for Sybase too, and presumably for any
>other DBMS that uses raw devices.
>

True.

Solaris 2.4 = 4K
Solaris 2.5.1 = 8K
Solaris 2.6 = ??
Solaris 2.X + Disksuite = ??K

I always use between 50 and 100K, whatever make the chunk size a
multiple of 100K.

>Neil Truby
>Londis Stores
>Hampton Hill, UK
>

--
David Williams

[wwa...@erols.com]

Yes you should always use on offset for creation of the chunks...in aix
the first block of data on the lv contains the logical volume control
block...this is often corrupted by creation of db slices without using
the offset...it isn't that much data...better to be safe then sorry...we
are having a problem now because of not using the offset for the rootdbs
on one of our informix instances....it is really a pain in the arse to
move after the fact....set it up right the first time...saves headache
later.

peace

walter walls