poor-mans cluster
Posted in Storage Applications, Advisor - Steve Rogers by Steve RogersReceived a question from a customer who has two standalone servers, each setup with a hardware RAID 1 running SBS 2003 with Exchange and SQL. Their primary server is the operating server in a network receiving all the network traffic and the secondary is just a backup with no traffic. Wants to know if RAID 1 be setup between the two servers creating a real-time duplicate of the active server on the backup server? If so, what hardware would I need to accomplish this?
Ideally, you would want a two-node cluster. You can accomplish this using your local disks you have today or you can move to consolidate and centralize your storage pool, ie: by using either FibreChannel or a less expensive iSCSI target Appliance.
If youstay with the traditional block storage configuration, you will need a clustered file system- ie: Microsoft clustering services, or Symantec Storage Foundation Cluster File System, to manage the data access between the two nodes and ensure the data stays in sync and consistent at both nodes. Mind you, using the Symantec clustered file system is an expensive proposition.
Alternatively, if you want what I call a “poor-mans cluster,” you can go to a common storage pool on the network; you will need a combination of your Microsoft SBS server, Symantec Storage Foundation™ 4.3 standard edition for Windows, in order to use Microsoft Dynamic Disks ( yes, it supports Dynamic Disks…read the web) and an iSCSI target appliance. These will allow you to create an active RAID 1 mirror for both applications for the primary server, and provide a passive iSCSI mount, when you need to, to the other server should the primary server fail.
You can purchase an iSCSI target appliance, might I recommend a Snap Server 500 series? (shameless plug…) or any other iSCSI unit for that matter.
First, I suggest you continue to keep your local disk mirrors on each server for your Exchange engine and SQL engine and Microsoft SBS operating system. You should create separate and distinct iSCSI mirrored pairs, one for the Exchange message store, and the other pair for SQL Databases.
You can use the Microsoft iSCSI SW initiator or a HW initiator - like the Qlogic QLA4050C. Attach these LUNs with the iSCSI initiator and then use the Symantec Storage Foundation Manager to configure these iSCSI LUNs as dynamic disks; then create a RAID 1 volume between each pair of LUNs.
With these redundant mirrored pairs established, you will then migrate the Exchange message stores and the SQL databases to the appropriate mirrored drive pairs. Both of these applications have migration utilities for doing this.
These RAID 1 mirrored pairs will now automatically and transparently failover should one LUN fail.
The other passive server can also mount these iSCSI LUNs on the iSCSI target, in the same manner, should the primary SBS server fail altogether.
SR
December 19th, 2006 at 2:53 pm
Hello Steve,
…
I am trying to put together a “tight-customer cluster”, similar to your “poor-man cluster”
It will run sql server cluster active/passive (2 nodes server), so I need a storage for db data on a shared bus.
- Could you please advise on necessary hardware?
- Is the Symantec Storage software necessary?
Microsoft technet says there is a need of a shared disk so that db data can be accessed by both servers but one at the time.
Thank you.
Regards
January 2nd, 2007 at 10:05 am
Any suitable iSCSI target will do here. It is a matter if your budget and what brand you would trust. Many companies now offer iSCSI targets; as does Adaptec, Snap Servers.
Symantec is not needed if you don’t have to use dynamic disks. for clustering support, setting up the iSCSI LUNs as basic disks is probably all you need to do. looks like they support up to an 8-way cluster with their SW iSCSI initiator
Microsofts link on clustering with iSCSI
http://www.microsoft.com/WindowsServer2003/technologies/storage/iscsi/iscsicluster.mspx
January 7th, 2007 at 7:35 am
You could also create a real time mirror by virtualizing your iSCSI targets into a common pool using software from DataCore and simply doing copy-on-write to multiple targets.
Alternatively, look at UDP, which unlocks the multicast functionality of IP, and lets you target two or more storage devices by their IP addresses for every write.
Also, I believe that NFSv4 with extensions will provide parallelism, if you want to use that instead of CIFS, for your Exchange-to-NAS architecture.
January 9th, 2007 at 8:07 am
Yet another low cost approach: a SAS-SAN, i.e. a Box with RAID controlers and disks connected with extrenal SAS cables. En example would be the Dell MD3000, 15 SAS drive slots, redundent controlers, power, etc. and 4 port of 4-lane SAS (12Gbps) that connect to SAS-HBA’s in the servers.