topic Re: OpenVMs v7.3-2 | Cluster+Oracle| Write back to Write-through in Operating System - OpenVMS

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

Hejib — Mon, 02 Mar 2009 16:06:36 GMT

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.

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

Volker Halle — Mon, 02 Mar 2009 16:53:42 GMT

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.

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

Hejib — Mon, 02 Mar 2009 17:26:32 GMT

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.

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

Hejib — Mon, 02 Mar 2009 17:33:40 GMT

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!

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

Paul Jerrom — Tue, 03 Mar 2009 00:35:01 GMT

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

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

Guy Peleg — Tue, 03 Mar 2009 06:46:05 GMT

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

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

Hejib — Wed, 04 Mar 2009 13:54:19 GMT

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.

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

Hein van den Heuvel — Wed, 04 Mar 2009 14:11:15 GMT

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.

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

Hejib — Fri, 06 Mar 2009 18:00:00 GMT

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