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author's profile photo Former Member
Former Member


Our company has two sites, distance between the two sites is about 600 KM and LAN is 20 Mb/s.

On the main site we run SAP R3 Enterprise 4.7 on Oracle 9.

Management wanted to have another Productive machine on the second site

So if one machine is broken the other should automatically continue the process within a minute.

Additionally someone said, if LAN is down both machine should continue to work on each site and as soon as network is up, database should automatically replicate each other.

Technology freak say we could use I-SCSI to replicate the two databases

Seems to be a nightmare. Does anyone have an idea?

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  • author's profile photo Former Member
    Former Member
    Posted on Sep 12, 2006 at 09:14 AM

    Windows or Linux?

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    • Former Member Former Member

      well for all those who are not familiar with ISCSI:

      ISCSI is a special protocol which implments the SCSI Protocol on Top of the TCP/IP protocol.

      Several network storage vendors are offering their storage products with an ISCSI interface (currently device drivers acting on existing NICs (Network Interface Cards)), Microsoft offers a device driver (Microsoft ISCSI Initiator, freely downloadable) which allows you to use ISCSI disks via existing Host-NICs. In some near future we will see hardware which directly implements the ISCSI Protocol.

      You can currently use ISCSI to build Windows Clusters (MSCS) with more than 2 cluster nodes. But the cluster is not what you need to use for what you want. MSCS is a shared nothing cluster (only one Clusternode can own a Cluster Resource at the same time). Also one of the basic restrictions in MSCS is, that you can only use the windows basic disk type. Dynamic disks can currently not be used as shared disks. But dynamic disks would be the prerequisit to build mirrored disks sets when using operating system mirroring.

      Without MSCS it is possible to mount the same ISCSI device on more than one machine, but this is totally unsupported - in theory it would be possible to switch off all caching and then both hosts would have the same view on the disk - but you will loose all performance.

      Network Appliance does recommend not to have any switch between the ISCSI Host and Client - I dont think that you will have an unswitched Network to the 2nd destination in about 600 km. The also strongly recommend (I too) to use at least 1 GB ethernet connection between the components using ISCSI. they also recommend to use fiber channel attached storage connections for productive databases.

      I don't think that ISCSI is useable at all for your needs and the solution will be more expensive if you will put the functionality to the storage level.

      Look for Standby Database functionality with log-shipping, contact storage vendors (like Network Appliance, EMC, or the big Hardware Vendors HP, Sun, IBM and ask them for disaster tolerant network based storage solutions), you may search for geospan clusters (geographically spanned clusters). They have a whitepaper for it, defining limits (max. latency) for MSCS which I think will not allow 600km between the two locations.



  • author's profile photo Former Member
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    Posted on Sep 27, 2006 at 02:59 PM

    You have to look for a solution which is based on for instance Hitachi TrueCopy/Async or IBM PPRC/XD. Or a software based solution like Oracle hotstandby database. MSCS is meant for hardware failures; not datacentre disasters.

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