Re: ASM Host Mirroring
- From: "Roman Podshivalov" <roman.podshivalov@xxxxxxxxx>
- To: "LS Cheng" <exriscer@xxxxxxxxx>
- Date: Tue, 19 Feb 2008 17:03:18 -0500
Hi,
Preferred read in 11g was to address the issue with stretched clusters in
order to avoid reads from remote storage.
But anyway back to original subject. If ASM sees both of your storages
separately and you are using ASM to mirror them - yes, ASM will issue two
requests for each write and single request for read. In 10G there is no way
to control which mirror will be read.
Both write request will be issued by ASM and carried over to local and
remote storage by means of configured transport (iSCSI, SCSI over fiber,
etc). There is no miracle there, unfortunately.
--romas
On 2/19/08, LS Cheng <exriscer@xxxxxxxxx> wrote:
>
> Hi Roman
>
> This will be a two node 10gR2 RAC set up. So no preferred read :-(
>
> Imagine the write request comes from node 1, i.e +ASM1, so ASM1 will issue
> one write request in local SAN and the other remote? How about reads?
>
> Looking soe stretch cluster setup diagrams with host based mirroring t
> gives impression that when write is requested from one node, that node
> writes locally and send a request thorugh some sort of network to remote
> node.
>
> Thanks
>
> --
> LSC
>
>
>
> On 2/19/08, Roman Podshivalov <roman.podshivalov@xxxxxxxxx> wrote:
> >
> > Hi,
> >
> > If I got the question right - ASM will issue two write requests to
> > separate controllers/ports your arrays are connected to. It's same as any
> > other software based LVS - no tricks there. 2 mirrors 2 write requests.
> > Starting with 11g you can define preferred mirror for read requests if I
> > remember correctly.
> >
> > --romas
> >
> >
> > On 2/19/08, LS Cheng <exriscer@xxxxxxxxx> wrote:
> > >
> > > Hi
> > >
> > > Does anyone know how ASM does host based mirroring. For example we
> > > have two storage arrays with 10 metres distance, two failure groups are
> > > created, one per array. How does ASM mirror the extents? Network? Using
> > > the
> > > Cluster Interconnect? Or a seperate Network?
> > >
> > > Cheers
> > >
> > > --
> > > LSC
> > >
> > >
> >
> >
>
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