HP StorageWorks MSA 1000 with Windows 2003 4

[AdilM]

We purchaced a SAN (HP StorageWorks Modular SAN Array 1000) because we want to share data, however after we install it and connect it to two servers running Win 2003, we found that when both servers try to connect to the storage at the same time data is corrupted. The reseller said this is by design, but I suspect it. How could I configure both serves to access the same storage without installing a third party software? I tried MS Cluster Server, but it only allows one server to access the storage while preventing the other. This is our first work with SAN.

Thanks

 

[comtec17]

Two hosts will never be able to access the same LUN/Volume at the same time without corruption. You will have to create seperate LUNS/Volumes if you want 2 hosts to have storage from you Array.

 

[AdilM]

Thanks for claifying this. I thought SAN was created to allow data sharing! Any idea what cluster solution to use for Windows to share the same voulme? I found some clusters for windows, but they depend either on mirroring or replicaion. I read that such a cluster must use DLM (dynamic lock manager).

Thanks

 

[comtec17]

You can use MSCluster but the volume must be used only in an active/passive state, it cannot be active/active to the same LUN or Volume.

SANS are used for Faster and Centralized Storage.

 

[AdilM]

Hi All,

One final question. Is there any one using cluster solution for Windows other than Microsoft Cluster Server? We need the ability to access the same volume by more than one machine at the same time. Unix clusters (e.g Veritas) do that.

Thanks.

 

[comtec17]

Why would you need the ability to have 2 hosts access the same volume? Could you please clarify your needs.

 

[AdilM]

Well, we are using some sort of Windows mail server that uses the "maildir format" to store messages to a central directory that is composed of a subdirectory for each user and one file for each message. The good thing about "maildir" is that it doesn't require locking any file (Different delivery processes never touch the same file), so more than one server can write to the same central mailbox directory. (

http://www.qmail.org/man/man5/maildir.html)

This is good for load balancing specially if there is huge mail traffic. We are storing the mailbox directory at a dedicated server and have two servers accessing it through shared drives. We want to put the mailbox in a central storage for efficiency and redundancy.

By the way, one of our mail server community is using NAS for the same purpose and below is what he wrote to me:

"We use Netapp filers (NFS/CIFS) and have no problems sharing data between multiple servers simultaneously, even when combining Unix and NTFS filesystems. Half the idea of the NAS is so you can share data."

Regards,

 

[Rols]

In a SAN environment you cannot have 2 hosts having access to the volume at the block level (ie: the volume appearing locally on both hosts) at the same time. This is because there is no management layer to control the read / write access to the volume.

When using NAS you are essentially sharing a volume at the FILE level. It is a network share there for the read / write access is controlled by the device that is sharing the volume. ie: Windows server or NAS appliance etc.

 

[Chacalinc]

AdilM,

The only "real" cluster that I know is "Oracle Real Cluster", and it has the feature to share the same data with 2 or more servers... but it is a Oracle feature. All the rest of cluster are actually "failover".

There are some kind of filesystem where you can share the same lun between 2 or more servers, example: OCFS (Oracle File System), OpenGFS (for linux/unix).

What you need for your mail app. is NAS, and how your are working right now (Win server as file server) fits for you, however you can think on a NAS because it is manufactured to be only FileServer, so it has better performance than a W2K server.

 

[AdilM]

Rols
Chacalinc

Thank you. I have better understanding of the subject now. We will use the NAS with MS cluster for failover only.

Best regards,

 

[Chacalinc]

If you going to use NAS, why you want MS Cluster? If you have qmail, both servers can access the NAS at the same time... you don't need Cluster (or failover), you need both servers active.

BTW, I have a customer with some mail server as you describe... it is a good mail server, the problem is to backup the mailboxes, files are usually too short so you have performance problems to back them up.

Cheers.

 

[AdilM]

Chacalinc,

The original idea was to have the NAS and let both servers share it. My company chose this StorageWorks NAS based on that assumption. However it turned out that we cannot share it between servers, any server must has exclusive access to it. If another server access it at the same time, data will be corrupted. At this point when we started to think about cluster solution, because we cannot return the equipment to the vendor. We already have the two servers and NAS, so what can we do with them other than goup them in MS Cluster ?!!

 

[Chacalinc]

good point... it's a comercial issue, out of my technical hand.

But, if the storage is a NAS, why you can not share? it's out of the standars... are you sure this is a NAS? is it not a SAN?

Cheers.

 

[davidmichel]

Would it work if each system had it's own share on the NAS box via a mapped drive?

 

[Chacalinc]

David, you wrote:

"The good thing about "maildir" is that it doesn't require locking any file (Different delivery processes never touch the same file), so more than one server can write to the same central mailbox directory. (

http://www.qmail.org/man/man5/maildir.html)

This is good for load balancing specially if there is huge mail traffic. We are storing the mailbox directory at a dedicated server and have two servers accessing it through shared drives. We want to put the mailbox in a central storage for efficiency and redundancy."

NAS is designed to *share* data, so a NAS is a mapped drive for several servers in order to *share* data.

 

[AdilM]

Sorry I used the term NAS instead of SAN in the last two postings by mistake. We have (HP StorageWorks Modular SAN Array 1000). It uses Fiber Channel technology and each server sees it as a local disk, but the two servers cannot access it at the same time. There is no share for it (I least I couldn't find any) and going through manuals revealed no way to do so.

 

[fraxx]

The fact that two or more Windows hosts cannot successfully access the same volume at the same time is not something that's limited by this particular hardware. As you've already discovered, you will get corruption if you configure the system with more than one server to access the same volume _unless_ you use a locking mechanism. This is what MS Cluster service is; it locks the volume to one particualar host at any one time.
The hardware as such will happily share the volume(s) to multiple hosts, it's simply a matter of checking the wwids in the ACU utility.
For two or more hosts to have concurrent access to the same volume, the file system must be aware of this. NTFS is simply not designed around it. Therefore, not many applications could benifit from it either, unless they were highly specialized to take advantage of the concurrent access. Oracle RAC is one such example, as stated in a previous post.
I've done some research on the subject previously, and there are emerging products and companies that adress this issue. I have no idea on how well they work or how well they would adress your problem.
Some links:

http://www.polyserve.com/

http://www.sanbolic.com/

If you're looking at Linux and various flavours of Unix you might find better solutions, but that might also be outside your scope.

Unfortunately, the SAN concept is by many something "magic", and will be able to solve all sorts of problems. As it is now, it's not much more than SCSI devices on a network. In time, software and OSes will be "SAN" aware to take advantage of the technology. Just as it took a while to write software that was truly network aware when LAN technology became more common.
/charles