Continuous Access EVA

[Fernando Bandeira]

Hi

As i understand it, the point of DR Groups is to keep multiple copy sets consistent. So if you have an application that spans several vdisks, then they would all be placed in the same DR group. Amongst other things, this would ensure that they keep I/O ordering across all members of the DR Group. Problem is, you can only have 8 copy sets per DR group - so what do you do if you have an application that uses 10 vdisks, and needs to be replicated whilst ensuring I/O ordering?

Regards
Fernando

[Uwe Zessin]

Check if you can get the application to work with 8 Vdisks.

[Orrin]

Hi Fernando,

What is the application?

Regards,
Orrin.

[Matthias Rettl]

hy!

read the revision changes for eva vcs v3.020 - it's attached (don't ask where i got this engeneering announcement from :)

there are several improvements in continious access... maybe there are some that will help you with your problems.

regards,
matthias

[Fernando Bandeira]

Hi All,

Uwe - unfortunately we can't; expnasion is even planned for adding another 3 vdisks to the application.

Orrin - MS SQL

Matthias - Thanks for the document. However, there seems to be no improvement in the next VCS with regards to the limit of 8 copy sets per DR group.

[Uwe Zessin]

Can't you just increase the size of the Vdisks? I don't think you already present 22TB, do you?

[Fernando Bandeira]

The customer has been advised (not by me) that the SQL data LUNs should ideally not exceed 100GB. So right now there 6 data LUNs and two log LUNs. They intended to add more as previously mentioned.

[Matthias Rettl]

ok, hold the LUNs as low as you can. but if it's technically not possible, don't insistence on a value of "100GB". (a lower disk size, for instance, reduces the time for a chkdisk in case of a unexpected "shutdown" - i.e. bluescreen.)

enlarge the LUNs to a value that fits into your application needs. 100GB or 250GB... don't think about it.

[Uwe Zessin]

I agree that makes sense on a file server, but does SQL server store its tables in lots of small files? (honest question)

[Matthias Rettl]

no. but nevertheless, keep a a windows disk balanced between needs and free space. not 500GB when 10 are needed and not 100GB when 95 are used... thats what i wanted to say.

[Uwe Zessin]

Ah, OK. I read you were talking about CHKDSK, not overcommitted free space - never mind.

[Fernando Bandeira]

Thanks. I have spoken with the customer, and they are definately not wanting their vdisks for SQL larger than 100GB. I dont know much about SQL, so there is not much I can say or offer in that respect.

Looks like we will have to wait until the limit on copy sets per DR group is increased.

[Matthias Rettl]

hy.

hmm. could you ask them for the reason? maybe they have a reference to a ms knowledgebase article - i'm really interested. (otherwise i would not trust in a rumour that possibly comes from historical problems in elder versions of sql...).
which sql server version are you using?

regards