Thanks to the ff for their quick reply:
Dr. Udo Grabowski
Derk Tegeler
Udo de Boer
Jim Fitzmaurice
Alan (from Compaq)
All gave the same answer. I could have 2 different disks in a shared SCSI
bus mounted on 2 separate servers. This will not give any problem as long as
I have cluster software running. The cluster software will take care of
coordinating the bus sharing.
I'm attaching their replies below:
Regards,
Carlos
--------------------------------------------------
We essentially had the same problem. You cannot modify the same filesystem
from two different servers (actually, you TECHNICALLY CAN, but this will
corrupt your filesystem sooner or later!). What you need is synchronized
access as provided by the TruCluster Server 5.1 through the Cluster File
System. If your services filesystems are on two different disks, you can
modify them from both servers, but never one and and the same filesystem.
Dr. Udo Grabowski
--------------------------------------------------
Your config is fine. You will only have problems accessing the same SCSI
target from the 2 servers at the same time, most file systems will die.
Your only limitation is bandwidth on the controller accessed by both
servers.
Regards,
Derk Tegeler
--------------------------------------------------
It doesn't make a difference. TruCluster supports shared scsi busses. Look
in
the hardware manual for trucluster. It is very good and online on internet.
regards,
Udo de Boer
--------------------------------------------------
Sorry but your assumption is wrong. I have two separate Oracle processes
and numerous other applications using various disks on both shared SCSI and
a Shared FCAL. I have three systems in my cluster, and at any given time I
can mount any of the disks on any of the three cluster members and access
them at any time. The cfsmgr (Cluster File System Manager) handles the
access. In fact a System A can even get data from a file system mounted on
System B via the cfsmgr. ALL SYSTEMS in a TruCluster see ALL DISKS as if
they were mounted on that system, even if they are actually mounted on
another system in the cluster. Simultaneous access of disks by different
members of the cluster is all handled by the cfsmgr. As an example, my two
Oracle applications. One normally runs on Member1 and the other on Member2.
Both have the actual application data on the Shared SCSI, while the actual
databases are on the Shared FCAL. Both applications can be (and often are)
accessed simultaneously by multiple users. Nobody sees any problems, and no
error messages are generated.
TruCluster and cfsmgr are truly amazing. Plus if Member1 goes down, I
can relocated the application to Member3 and have cfsmgr automatically
remount the application related disks on that system. You should peruse the
manuals for TruCluster, its great they thought of almost everything.
Jim Fitzmaurice
--------------------------------------------------
The various versions of the clustering software have allowed
system to system failover by allowing disks to be on a shared
bus. The cluster software handles the coordination necessary
to ensure only one system can access a disk at a time. As
long as you use the clustering software to control access
to the disks you should be fine. If you're not using the
clustering software to control access, don't assume that
the operating system are doing something extra. They
probably aren't.
I think the method used by older clustering versions is
a SCSI Reserve command. This isn't persistent and won't
survive power failures (and probably bus resets). The
clustering software takes care of this. You could use
scu(8) to reserve a disk yourself, but you have to allow
for this lack of persistence.
Read the clustering and documentation. If doesn't say
that what you're trying is supported by it, it is probably
best to assume that it isn't safe to use. Without the
coordinated access, it is very to make one mistake that
can destroy all the affected data. The convenience may
not be worth the risk.
alan_at_nabeth.cxo.dec.com
----- Original Message -----
From: "Carlos Chua" <chuacarlos_at_hotmail.com>
To: <tru64-unix-managers_at_ornl.gov>
Sent: Monday, July 23, 2001 2:20 PM
Subject: 2 cluster services sharing the same SCSI bus
> Hi Gurus,
>
> I wish to seek opinions on the ff configuration:
>
> a) Environment is Tru64 UNIX V4.0E and TruCluster V1.5
> b) DiskA belong to ServiceA which normally runs on ServerA
> c) Likewise, DiskB belongs to ServiceB which normally runs on ServerB
>
> Question:
>
> If I place DiskA and DiskB on the same shared SCSI bus, will I be facing a
> lot of troubles in the future? I would assume if ServerA is accessing
DiskA,
> ServerB can't access DiskB. On such situation, will my error logs be
filled
> with error messages?
>
> Is it preferable that if I only have one shared scsi bus to run both
> ServiceA and ServiceB on the same server (assuming the server has enough
> horsepower)? or it doesn't make any difference at all?
>
> Thanks in advance for any opinions.
>
>
> Best Regards,
>
> Carlos Chua
> chuacarlos_at_hotmail.com
>
>
> _________________________________________________________________
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>
Received on Tue Jul 24 2001 - 13:00:44 NZST