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Re: [Xen-users] Planning - question about storage

Zoran PopoviÄ [11.06.2009 16:52]:
> 2009/6/11 Werner Flamme <werner.flamme@xxxxxx>
>> Hi everyone,
>> I am very new to Xen but will migrate 3 SAP ERP servers plus 1 SolMan
>> into a Xen environment next year, probably running Novell's SLES (as we
>> use SLES right now).
>> The machines will be app servers only, no DB - the DB is "outsourced" to
>> a common Oracle RAC this year (maintained by a colleague).
>> So I will get 2 boxes and now fiddle around with possible configuration
>> of storage. Due to SAP notes the SAP binaries must be stored on the RAC
>> and made accessible from there, for example via NFS or SAN. In our
>> company, we are used to SANing ;-), so my boxes will have some FC boards
>> to connect to the RAC's 2 FC switches. Am I right that I can access the
>> block device from SAN (will be one big thing with OCFS2) inside dom0 and
>> pass them via phy: to the domUs?
> Ok, I am just doing some testing on RHEL5.3 with Xen 3.0.3 (somewhat) on
> Itanium (IA64, not x64) Dom0 and HVM Windows Server 2003 HVM DomUs.
> Dom0 is booting and completely using FC SAN (HBAs), DomUs also use SAN -
> actually, I am using snapshots (EVA HP split mirror terminology) of the
> production database which I easily present to Dom0 and use it directly as
> phy drive on DomU. There I have SAP ECC6.0 EnhP3 installed together with
> Oracle db. I am very happy with results !! The only problem is
> I/O on HVM because IA64 lacks PV support at the moment. Currently, that is
> the only reason not to keep DB on HVM DomU (though there are many ways to
> somehow circumvent or lessen problems, apart from getting SAP's official
> permission/acceptance for the platform. Oracle VM is Xen, should I say more
> ...

So I am not the first one who tries to fiddle together SAP an Xen :-)

SAP does not allow Oracle VM for a productive instance, see SAPnote
https://service.sap.com/sap/support/notes/1122387, near the end.
CitrixXen is Xen also, but not allowed, a few lines above Oracle VM ;-).
They just don't pay SAP to test it, I think. Novell and RedHat did...

We use CitrixXen in our company for a variety of things, and if it was
allowed, I'd use it...

> But, one thing puzzles me - why would you access SAP binaries lying on
> Oracle RAC disks ? Standard failover SAP HA (High Availability scenario,
> either Windows or HPUX, most likely it is same with Linux, I didn't use or
> read about that so far) is using separate cluster (shared storage) disks.
> Using NFS for binaries is not an idea I would be eager to use. Also,
> accessing raw OCFS2 drive wihtout Oracle OCFS software on DomU (where dialog
> or centrral instances reside) makes no sense. If it is about Central
> scheduling for SAP (note 895253) NFS is ok, but for SAP kernel I couldn't
> find any note claiming this - can you show me the note ? 

This is something I read on one of the various PDFs on
- I think it was the first one, "SAP NetWeaver with Oracle 10g R2 RAC
(UNIX & Linux)". This document is spread by Oracle, too (not only by SAP

I have a paragraph on page 4 that reads:
This document assumes that the planned installation uses a cluster
filesystem for the voting disks, CRS repository, database files, control
files, redo log files, archived redo log files and executables under
$ORACLE_HOME (software installation directory for the Oracle RDBMS
software), log files and executables under $CRS_HOME (software
installation directory for Oracle CRS software) as well as all SAP
executables in the /sapmnt directory.

I understand this text so that /sapmnt has to be on the SAN too. What's
the big deal? I have it already running this way now with my SAP SAN ;-)
 BTW, we have only one instance per system, no separate dialogue instances.

> Using SAN FC
> usually involves availability and reliability mechanisms (multipathing, raid
> levels, etc), and OCFS is justified for other purposes e.g. you want
> patching kernel on one place, directory - but you have sapcpe for that, and
> you loose availability - concurent maintenance (all application servers must
> be put down). I would simply use Dom0's phy (SAN) drives in the DomU's most
> usual and convenient file system (you can even create f/s in DomU).
> I would be glad to help you if can or to know more about this,
> ZP.

Zoran, unfortunately the shared storage I will use is already formatted
with OCFS2 and used by the RAC for other DBs. I am not allowed to change
the partitions or filesystems in that thing, though I might be able to
do so ;-).

SAPnote 527843 (Oracle RAC support in the SAP environment) tells me that
- when I am using Linux - I have to use "Oracle Clusterware + OCFS2
1.4.x", so this is not a point of discussion here :-(

<mode="brag">Of course multipathing is (and will be) used, and the
shared storage isn't RAID-0 :-) There are two RAID boxes (12 Disks with
300 GB each) mirroring each other, to be more exact...</mode>

Thanks for your input!


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