Doubletake

davmac1

Is anyone using this software or anything like it?
It makes a mirror copy of the server on a disk block by block basis on to another server, so it can be used in case of failure.
It seems to me that a block level disk transfer has to have a noticeable affect on performance.
Unfortunately the server being protected is RAID 5 running SQL Server 2005 with OS, log, database files all on the the same RAID 5.
It is 64 bit SQL Server with 4GB of RAM. I can get them to double RAM.
Most of the time the buffer cache hit ratio is over 98%, but it has dropped occasionaly to 65% and some users have timed out.
It is a new install, so it will benefit from tuning, but I am wondering what impact Doubletake will have on it.

bbrown

davmac1 wrote:

...Unfortunately the server being protected is RAID 5 running SQL Server 2005 with OS, log, database files all on the the same RAID 5.
...

This is your first tuning issue.

davmac1

There is nothing I can do about the hardware - they bought it before I was brought in. They are bumping up the RAM to 12GB which would normally be overkill with the right hard disk config for 30 users and 18GB database.
Anybody witrh experience in using Doubletake? Will it hurt performance?

bbrown

Are you referring to the HP StorageWorks product?

davmac1

No - there is a company (Double-Take Software, Inc.) that has a product called Double-take with a web site doubletake.com.
It makes a failover copy of your Windows Server to another server.

I am looking for feedback from anyone who has actually used it.

Once again, the decision was made before I got involved. My preference would be for replication if a company thought it necessary to have a standby server.

David_Singleton

davmac1 wrote:

No - there is a company (Double-Take Software, Inc.) that has a product called Double-take with a web site doubletake.com.
It makes a failover copy of your Windows Server to another server.

I am looking for feedback from anyone who has actually used it.

Once again, the decision was made before I got involved. My preference would be for replication if a company thought it necessary to have a standby server.

Why can't they use log shipping?

bbrown

Or mirroring?

Marije_Brummel

We have some customers running Double Take with no problems at all. They use it for their entire system, not just SQL.

Next to doubletake we always use logshipping to protect data corruption since doubletake mirrors the curruption in a ms.

David_Singleton

Mark Brummel wrote:

Next to doubletake we always use logshipping to protect data corruption since doubletake mirrors the curruption in a ms.

Thanks for that, its actually a question I was asked by a client a couple of days ago. They were asking me why they would need log shipping if they have mirrored mirrors why do they then need log shipping, and this was the reason I was trying to explain.

Brennels

Double-Take is actually byte level replication which is much smaller than block level. Regarding overall performance, when mirroring you might see about 10-15% CPU utilization but during normal replication 5-7% depending on the amount of changes occurring. Double-Take has literally thousands of customers protecting SQL and from your post I don't think that is your issue but here are some tips.

- General SQL Tuning, The database and logs should be on separate drives and probably not a RAID 5. Depending on the activity of the database you may be running into disk speed limitations that are slowing the performance of the database down on increasing CPU. Moving the logs to a different drive or controller (other than C:) should help.
- Watch out for DBCC processes. I have seen SQL run scheduled maintenance that re-organizes the entire database and can take 4-6 hours or more to do this. During this time the logs are committed to the database, deleted, new logs are created, written too, etc. and the changes can be 4 times the size of your database. These are considered changes that Double-Take will replicate. If they are significant it may start writing the data to the cache which is probably located on the same drive as your database and log files and will just increase the overall disk utilization.

Using the Double-Take Application Manager for SQL is one of the simplest solutions and certainly working with log shipping or VSS snapshots is an option for additional recovery points.

Your customer is likely under maintenance and has 24X7 support and you can find more information on the knowledgebase or actually logging a call.

800-775-8674 or 317-598-2066 or find answers online at support.doubletake.com!

Hope this helps. - regards

davmac1

Thanks for your response - looks like you are in the same town as their headquarters.

This was a network services provider solution that we are having to live with. At least it is 64 bit. We cannot post any larger batches without timing out the web users coming though NAS.

We upgraded them from Navision database to SQL Server 2005 and are using SQL views for the web and NAS to enter the orders via codeunits.
The old Navision database server was running on SBS2003, so there has been an overall improvement.
The SQL Server box is poorly configured, but holding its own right now.