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OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

 
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Hejib
Frequent Advisor

OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Hi,
We've a cluster of ES80's, OpenVMS v7.3-2 running Oracle 8 & 9. SAN & disks on HSG80's. Just added some disks - have now spotted they're WRITE-BACK enabled, & the Oracle team want WRITE-THROUGH. The SET VOLUME/WRITETHROUGH will do this - are there any risks? Want to be really sure that it's o.k. to just issue command etc.
Thank you.
8 REPLIES 8
Volker Halle
Honored Contributor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Graham,

are you using Pathworks on this cluster ?

Did you read $ HELP SET VOLUME/WRITETHROUGH

This feature only affects Pathworksa d allows . The File Cache (XFC) is still writethrough anyway.

Volker.
Hejib
Frequent Advisor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Hi Volker,

Thanks for the reply - yes, I had read the help information.

However, that doesn't answer my question, which was can I issue the command on the fly, without causing a problem. My application is Oracle, rather than Pathworks.
Hejib
Frequent Advisor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Hi Volker,

You've made me re-read the Help, so actually the show /device/full output isn't meaningfull, as XFC sits in front of the disk anyway and as that's write-through it doesn't matter.

Which means it doesn't matter what write-blah this disk is in... I think that does answer my question.

Thank you Volker!
Paul Jerrom
Valued Contributor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

XFC is irrelevant.
What you want is write thru on the HSG controllers - right?
Then you need to connect to the HSG and do it there, can't be done direct from VMS.

BTW, as an aside, there was a rumour about 10 years ago that write thru cache and Oracle didn't mix, but that turned out to be a mix-up between Oracle and (then) Digital pre-sales folk. Oracle and write thru are fine.

have fun
PJ
Have fun,

Peejay
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If it can't be done with a VT220, who needs it?
Guy Peleg
Respected Contributor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Graham,

You should be focused on the HSG and not
on the operating system. Oracle marks all
I/O NOCACHE so it bypasses all O/S caching
completely.

Enabling write back on the HSG should be
okay assuming you have a battery to backup
the HSG cache.

If this reply does not answer your question
let me know.

Guy Peleg
Maklee Engineering
http://www.maklee.com
Hejib
Frequent Advisor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Hi Guy,

Yes, we have battery backup on the HSG's - and all are working.

My customer wants the disk to be (from OpenVMS) mounted /WRITETHROUGH - so can I do a simple SET VOL/WRITETHROUGH with the disk 'live' and mounted in the cluster?

I believe I can do this, as it's a valid command, and VMS rarely allows you to do something that'll screw up a working system.
But I'm after validation.

Thank you.
Hein van den Heuvel
Honored Contributor
Solution

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

Just use set volume for the write-through'.
No need to re-mount.

$ ld connect lda4.disk lda4:
$ moun/over=id lda4:
%MOUNT-I-MOUNTED, LDA4 mounted on _$8$LDA4: (TD183)
$ pipe show devi lda4:/full | searc sys$pipe write
write-back caching enabled.
$ set volu/write lda4:
$ pipe show devi lda4:/full | searc sys$pipe write
write-through caching enabled.


It's not going to make a difference, other than make an insufficiently informed happy.

Write-through is indeed what is needed for Oracle, but it is already happening.

Write-through is was Oracle explcitly requests for the data anyany, as Guy already mentions.

Write-through through is what everyone gets anyway, data and file system info (headers).

I should perhaps re-investigate, but best I recall the Write-back setting does not turn that on, it just allows applications to request it, if they know how.... Pathworks used to know how.

Go for it!
Hein.
Hejib
Frequent Advisor

Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through

All resolved, as expected. Thank you for your assistance.