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Synchronous replication between 2 SANs

J

Jay_2

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Mar 20, 2006
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I am looking at installing 2 SANS 1 at HQ and 1 at our new branch office, I would like 2 way synchronous replication so we always have the same data on the SANs in each location for DR and also to split the load on our database servers.

I have a few questions though

1 Can synchronous replication replicate files that are in use such as databases

2 is mirroring a better option for databases?
 
It sounds like you want a multi-master setup. I do not know about anyone who provides a true multi-master block level synchronization. If it exists, it would be extremly expensive.
 
The issue we have here is that we are stuck on SQL 2005, we need active active replication of SQL databases we also need active active replication of users files. We are splitting a Citrix Farm over two sites so we need the same data on both sites at all times. This helps with DR as well.
 
A grid-array based SAN implementation should accomplish what you need. This would not actually provide 2-way synchronous replication between SAN's, but it would actually split your SAN's across the two sites, with data spread across the SAN units at each site. This way each site is actually accessing the same data. With the right amount of units at each site, if you last Site A, all data can still run from site B and vice-versa. You need a lot of bandwidth between sights with very low latency for this to work.

Something like the HP P4000 G2 LeftHand SAN would be an option.

I'm not sure if something like MetroCluster from NetApp would do what is necessary based on your description, but that's another think to take a look at as a starting point.

It's not strictly about the storage units doing synchronous replication on the data sits on them. You have to look at the data being accessed on those devices, and what happens when User 1 needs to access data on SAN 1 at te same time User 2 needs to access the same data on SAN 2, make changes, and then merge them. This typically puts in you in the siutation of needing to rely on the software application layer handling your data replication, and not the storage array.
 
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Funny you should talk about Metro Cluster I am just looking into that at the moment.

Latency could be an issue it may be upto 40ms at times, both ends are 100Mbps leased lines but latency is always a tough one.

Can anyone else think of a way to replicate these SQL databases to allow us to split this Citrix farm into 2 zones?
 
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What actual SQL databases are you concerned with? The ones the Citrix Farm use to hold config and reporting data, or application level?

Have you ruled out just having the "remote" site Citrix server applicaitons access the databases in the primary site? Not enough bandwidth or something like that?
 
We have apps that need access to SQL databases. We would like to split the load for DR mainly and also it gives us the ability to take one site offline when we need to.

We where going to create one zone across the two sites and the users can hit any of the Citrix Servers on either site and have access to the same apps and the databases.
 
So if I understand correctly you have Site A and Site B .

On Citrix servers at Site A, you have Application A and it uses SQL DB A
On Citrix servers at Site B, you have Application A and it needs to SQL DB A

So at both sites, the same app and the same DB, and the DB data needs to be identical, real time between sites. Correct?

In that model, you think you're going to end up being defined by whatever SQL can do at the application level. Because as I said earlier, it's not as simple as a SAN replicating the data that sits on it . Since both sites would modify the SAME SQL DB ,you need to deal with merging changes, lockout of records, etc. I think (not 100% certain) that's outside of the realm of what the SAN software itself can do itself. It may be a combination of SAN software interfacing SQL features that can do it, but again, not sure.

If you have a relationship with someone like a CDW or PC Connection or PC Mall, I would call up your rep and get the storage guy on the phone and get some details from someone who knows a big range of products.
 
Thanks for the input, I have some Dell guys, HP guy and NetApp guys calling tomorrow so I will see what they come up with. I hope you can see how fantastic this would be if we can pull it off.
 
Yeah, you want the HP option, best price.

Hope your site-to-site has latency<=1MS, otherwise your throughput goes to shit. Knew a company trying to get site-to-site replication from Minneapolis to Chicago over 18ms pipe, took 1gb/s connection down to 340mb/s
 
He said in an earlier post he has 100mb, but latency could go up to 40ms. In general, that's too high of a latency to use a grid array approach across multiple sites, 100mb is probably going to be o thin as well.. Usually you wnat something like 1gbps with no more than a few ms of latency for it to actually all work and feel like storage is local to both sites. The HP specialists said they see this approach used more in customer owned sites where they either have their own dark fiber and can guarantee connectivity end-to-end, as running through carrier network with tons of bandwidth can be a crapshoot due to the latency factor.
 
Why aren't the applications for site A just hosted there as seamless apps to site B.

Set up 2 Citrix farms, and have both farms xml services listed in the pnagent config at the local site?
 
He wants the data access to the SQL DB's that the apps access to be local to the site in which the application launches. It's not any kind of Citrix issue really, it's a design preference on where the application data is held and accessed.
 
You may want to look into something like EMC's VPLEX Geo, not sure of your budget, however.
 
I just bought a SAN- everyone I talked to had a hex on EMC.

We went with an Equalogic.

We'll be working on a similar DR option next quarter, 2 sites (Phoenix, Dallas)- looking forward to seeing what you come up with.

I've got a great SAN guru that I worked with at Dell for what I eventually bought if you want their info.
 
Decent read on EMC VPLEX here (doesn't talk about Geo, but it helps you get a general understanding), to get an idea of what it offers: http://www.serverwatch.com/hreviews/article.php/3883466/EMC-VPlex-Buyers-Guide.htm

It is certainly designed to accomplish what you need, but you can see how much it costs. It's also NOT your storage, it's something you stick in front of your storage. Also, like other potential options that have been mentioned, speed/latency/distance are all critical factors in being able to use a solution like this.
 
bloody hell! thats expensive!

jen4950 said:
I just bought a SAN- everyone I talked to had a hex on EMC.

We went with an Equalogic.

We'll be working on a similar DR option next quarter, 2 sites (Phoenix, Dallas)- looking forward to seeing what you come up with.

I've got a great SAN guru that I worked with at Dell for what I eventually bought if you want their info.
Click to expand...

Its looking very very hard to do if you want live data on both ends, not so hard if its just DR though.
 
"Anything is possible with enough money"

But everything is always relative. As an example, If you determine it's too expensive tohave live duplicate data at both sides, you may find out you need more bandwidth to do what you want to do with all data at one site, then you are paying more per month for bandwidth. That's now a cost analysis item over upfront costs of hardware/software + recurring yearly maintenance.
 
yes, I think I am going to split the citrix farm and run some services on one and some on the other with regular replication between them. If we do have a disaster then we can switch all users to one site but some may lose 1 hours worth of data.
 
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