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MSA 500 G2 with 4 nodes

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Scott Moring
Occasional Visitor

MSA 500 G2 with 4 nodes

I have an MSA 500 G2 with the high availability kit. I have 4 servers accessing to the SAN with 2 volumes created. All 4 servers are running WIN 2K3 R2. 2 of the servers are IIS, and 2 are SQL 2005 servers.

I continue to get NTFS errors, (Event ID 55) with data corruption, but no apparent data loss. This always requires a reboot with an offline CHKDSK operation. This fixes it, but the problem returns within a few days.

Currently there is light usage of any of the servers, but that is about to change, and I need to track down this problem. I have not been able to create the problem myself, and cannot pinpoint any particular process that is causing the errors.

I would appreciate any advice on this problem!

Thanks
6 REPLIES
Sandy Chen
Honored Contributor

Re: MSA 500 G2 with 4 nodes

Hi,

Can you let us know what is your LUN Raid level, your multipathing software (securepath etc, and it's version).

How do you zone the SAN switch and SSP on the MSA?

Is this 2 LUN is shared between this 4 servers??

Regards,
Sandy
I never think of the future. It comes soon enough.
Scott Moring
Occasional Visitor

Re: MSA 500 G2 with 4 nodes

The SAN is RAID 5 with a Hot Spare.

I am not running the Multipath Software because it is not setup Multi-Path.

There are two volumes set up, and all 4 nodes can see both volumes.

Not sure what you mean by Zoning. I do not have SSP enable right now, but am considering it.

Currently each of the servers runs a 642 SCSI card, and they are attached to the MSA.

It is a 4 LUN card in the MSA, so each node has it's own connection to the SAN.

I hope that helps.

TIA
Stephen Kebbell
Honored Contributor

Re: MSA 500 G2 with 4 nodes

Hi,

first things first: you have an MSA500, which has nothing to do with SAN. It's a shared SCSI Box, so you can forget about SAN Switches and zoning. Multipathing is also not relevant here, as you have 4 servers with 1 SA642 in each, so it's all single path.
You say you have 2 SQL servers and 2 IIS servers - are they clustered? If not, SSP will not help much, although you should use it anyway. 2 or more standalone windows servers CANNOT access the same LUN, as it will lead to data corruption. You either need to cluster the servers (1 cluster for SQL, 1 cluster for IIS), or use a shared filesystem like Polyserve.

Regards,
Stepohen
Scott Moring
Occasional Visitor

Re: MSA 500 G2 with 4 nodes

Thanks for the info Stephen.

You say that all 4 nodes cannot access the same LUN without data corruption. Does that hold true even if I set up SSP and 4 partitions on the volumes? So that each node has it's own volume and can't see the others.

I know clustering will accomplish this as well, but I don't want to go that route if I am not forced to. Even setting up SSP will present it's own drawbacks to what I am trying to accomplish.

Thanks again
Stephen Kebbell
Honored Contributor
Solution

Re: MSA 500 G2 with 4 nodes

Hi Scott,

if you create 4 logical drives on the MSA500 and use SSP so that each server sees only one logical drive each, then you are fine. Using just Windows partitioning won't work.

NTFS is not a shared file system. If you had the same volume presented to 2 servers, if one server writes data to the disk, the other one will not see these changes (unless you reboot it). And because neither server knows about the other, they both assume they have exclusive block-level access to this disk. Both servers could end up writing different data to the same blocks, thus resulting in data corruption. In a normal Windows Cluster, the cluster locks a disk so that only one node has access at any particluar time.

Regards,
Stephen
Scott Moring
Occasional Visitor

Re: MSA 500 G2 with 4 nodes

Perfect! This is the information that I needed. I had a feeling that was what was going on, but wanted more confirmation.

Since I really would rather NOT have to separate into 4 volumes (I know I used the word partition, but I meant volume) I will most likely go to clustering.

Thanks again!