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SQL Server SAN Migration 8/25/2009 11:16:01 AM

SQL Server SAN Migration

I think this is my 3rd or 4th SAN Migration casued by:
 - completely moving data centers
 - changing the storage backends to different vendors
 - consolidating SANS
 - growing to a bigger san to consolidate more

There are several different scenarios to consider
 1.  Stand alone SQL Servers Instances on Internal Disk to SAN
 2.  Stand alone SQL Servers on SAN Disk (changing sans).
 3.  VM Ware SQL Servers (required to be on SAN)
 4.  Microsoft Clustered SQL Servers
 5.  Polyserve Clustered SQL Servers
 6.  BCV's / SAN Mirroring / replication technologies
The most important thing to remember is to backup.  The next most important thing, no matter what the SAN Engineers, Windows Engineers or Vendors tell you about SAN Migration, YOU AS THE DBA ARE RESPONSIBLE.  Understand the migration plan for each scenario, regardless of what anyone says, the DBA is always left holding the bag.  If you don't understand the migration plan / scenario, make them explain it, learn it, try and practice it.  I'll explain with an example. 

One of the important items in most scenarios is updating to latest drivers and versions of software, even this step can be dangerous.  In a recent effort to patch servers to the latest version of drivers the SAN disk just "disappeared", when it came back, there was NO DATA.  No amount of research could yield what happenned to the data.  Refer back to the most important thing!

All of the different scenarios are simple, with careful preperation and a good windows and SAN team. 

1.  Stand alone SQL Servers instance on Internal Disk to SAN.

Usually the most difficult thing here is that you are taking an existing stable server and adding a lot of new complexity to it.  Drivers and hardware for the SAN, sometimes this does not always go well, if possible I try and get new hardware and completely swap the machines, configuring the new machine in advance for the SAN and installing sql; taking several dry runs to ensure it's stable.  The next issue is the down time in copying the data from the internal disk to the san.  Than switch the drive letters and start SQL.  Don't forget the most important thing.

2.  Stand alone SQL Servers on SAN Disk (changing sans).

Here is where having a good windows and san team can help you.  Most of the migrations I've been involved with the Windows and SAN team will setup a mirror between the SANS.  Than on migration day we stop SQL Server, the windows and san team ensure the mirror is up to date, than split the mirror and hook the server up to the new storage and ensure the drive letters and mount points come up.  SQL DBA restarts sql, boom, your done.

Sometimes if your switching san vendors, you can't setup a mirror.  Now things get dicey.  Can you get "hooked" up to both sans simultaneously, of so than your ok, stop sql, copy the data to the new san, reset drive letters and mount points, restart SQL. 

If you can not get "hooked" up to both sans simultaneously than you need to default to some type of backup and restore mechanism, tapes or copying sql files to local disk (if you have room).  I'm usually not a fan of this, as I find that different vendors use different drivers, switching vendors means now you have both vendors drivers on the machine, the machine decays and becomes unstable, NOT FUN.  Don't forget the most important thing.

3.  VM Ware SQL Servers (required to be on SAN).

These have been my easiest san migrations.  That's because we have awesome dedicated VM Ware administrators.  They do it all, just schedule the outage.  But trust me, Don't forget the most important thing, check your backups went to tape, double check your Disaster Recovery plan.

4.  Microsoft Clustered SQL Servers

I've only done Microsoft Cluster migrations with SAN Mirrors, and it has been uneventful.  This is because the "mirrors" end result is the preservation of clustered resources (quorum), drive letters etc.  But don't forget the most important thing.  Again a great windows and san team makes this easier.  I'd fret to switch vendors on the Clusters, but if I ever do I'll update this post.

5.  Polyserve Clustered SQL Servers

This is the SAN Migration worst case scenario, "The clustered file system".  Below are the steps we followed for migrating sans with Polyserve.  Don't forget the most important thing.

-Dump vsql and vsqlinstance information from cluster
 -mx vsql dump >> vsql.txt
 -mx vsqlinstance dump >> vsqlinstance.txt
-Get a listing of all storage by copying the grid on storage summary to excel
-stop and disable all SQL instances and VSQLs
-copy the virtual root for each sql server instance to another server (outside the cluster)
-deport ALL dynamic volumes (paths are automatically unassigned)
-stop cluster services on all cluster nodes
-copy the entire c:\polyserve directory to another server (outside the cluster) for each machine (CYA)
-manage the storage to unpresent all LUNs from the old array
-break the mirror relationships and then present all of the mirrored LUNs
-create three new 1GB LUNs on the new array and present them for new mem parts
-put partitions on the three new LUNs
-go into the config utility on node 1 and delete old membership partitions and add the three new membership partitions
-start cluster services on this node
-export the config to other nodes and start the service on the rest of the nodes
-import all importable dynamic volumes
-assign paths
-enable instances and vsqls
Polyserve SAN Switch.doc (29.5 KB)


6.  BCV's / SAN Mirroring / replication technologies

Administring the advanced SAN technologies is different for each vendor and quite proprietary.  You definetly want to test and work with each one individually and ensure it all works.  The details of this are far outside the scope of a simple blog post, but having great SAN engineers will make this easy, as they generally setup the mirrors, clones and movement of them to different machines or remote locations.

Don't forget the most important thing.

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