September 28, 2011 at 12:02 pm
We have 2 server sites, our home office and our DR site. The principle database will be located on a server in our home office. The mirror will be located at our DR site. Where should my witness go? Does it make more sense to put the witness on a server in our home site or in our DR site? If our home site loses power, and the principle and witness databases are here, will the mirror know that it needs to become primary?
I'm just looking for best practice and guidance. I've done mirroring before, but only without a witness.
September 28, 2011 at 2:07 pm
Keep the witness in the same site as your principal database. If the principal loses connection with both the witness and the mirror the principal database will become unavailable. This means an outage at your DR site could cause a production outage to the principal database as well.
September 28, 2011 at 2:15 pm
JeremyE (9/28/2011)
Keep the witness in the same site as your principal database. If the principal loses connection with both the witness and the mirror the principal database will become unavailable. This means an outage at your DR site could cause a production outage to the principal database as well.
But if the witness and the principle become unavailable, the mirror will automatically realize it and become the principle?
September 28, 2011 at 2:23 pm
But if the witness and the principle become unavailable, the mirror will automatically realize it and become the principle?
No, there needs to be a quorum for automatic failover to happen. Here are a couple of msdn articles that explain the quorum's needed and how the witness affects the database's availability. These articles can explain better then I.
September 28, 2011 at 2:28 pm
Jeremy,
Sorry, but frankly I confused with your recommendation "Keep the witness in the same site as your principal database"
(and certainly I know that per BOL MS "We strongly recommend that the witness reside on a separate computer from the partners.")
But in case when Principal and Witness servers reside on the same location and power outage happened there is no more quorum and Mirror server has no idea that failure occurred? Or am I missing something in your logic?
IMO in this scenario (only 2 servers available) Witness should be on Mirror side.
September 28, 2011 at 2:37 pm
Yuri55 (9/28/2011)
Jeremy,Sorry, but frankly I confused with your recommendation "Keep the witness in the same site as your principal database"
(and certainly I know that per BOL MS "We strongly recommend that the witness reside on a separate computer from the partners.")
But in case when Principal and Witness servers reside on the same location and power outage happened there is no more quorum and Mirror server has no idea that failure occurred? Or am I missing something in your logic?
IMO in this scenario (only 2 servers available) Witness should be on Mirror side.
Reading the original post I assumed (possibly incorrectly) that there would be a principal server, witness server, and a mirror server for a total of 3 seperate servers.
September 29, 2011 at 7:04 am
JeremyE (9/28/2011)
Yuri55 (9/28/2011)
Jeremy,Sorry, but frankly I confused with your recommendation "Keep the witness in the same site as your principal database"
(and certainly I know that per BOL MS "We strongly recommend that the witness reside on a separate computer from the partners.")
But in case when Principal and Witness servers reside on the same location and power outage happened there is no more quorum and Mirror server has no idea that failure occurred? Or am I missing something in your logic?
IMO in this scenario (only 2 servers available) Witness should be on Mirror side.
Reading the original post I assumed (possibly incorrectly) that there would be a principal server, witness server, and a mirror server for a total of 3 seperate servers.
Jeremy, your assumption is right. There will be a separate principle, witness, and mirror server, but only 2 site locations for the 3 separate servers.
September 29, 2011 at 7:24 am
JeremyE (9/28/2011)
Keep the witness in the same site as your principal database. If the principal loses connection with both the witness and the mirror the principal database will become unavailable. This means an outage at your DR site could cause a production outage to the principal database as well.
The purpose of a DR site is to serve as a backup in case something happens at the main site. If there is a disaster at the main site (ie: power outage), we would want to make sure that we can failover to the DR site. If the principle and the witness reside at the main site, and become unavailable because of the power outage, we won't be able to failover to the disaster site, because the quorum would be lost.
Hmm...I don't think I am a fan of witness servers. It seems like it could do more harm than good.
May 3, 2012 at 3:27 am
I'm trying to work this out as well.
I can understand the problem with a production outage if the DR site goes offline, but if the mirror's at the principle location and that site goes offline, then you won't get automatic failover?
May 3, 2012 at 4:37 am
I use Database Mirroring with Witness for active/standby server
for DR site use storage replicate
May 3, 2012 at 6:49 am
Gazareth (5/3/2012)
I'm trying to work this out as well.I can understand the problem with a production outage if the DR site goes offline, but if the mirror's at the principle location and that site goes offline, then you won't get automatic failover?
I believe if you have the witness server and principal server in the same location and if there is a power outage, then mirror server will become the principal server......correct me if I am wrong....but if the mirror server cannot communicate to witness server/principal.....it should fail over automatically right?........then you need to manually script out the logins, alerts, jobs etc....at the mirror server.
Your thoughts.
TA.
Regards,
SQLisAwe5oMe.
May 3, 2012 at 7:09 am
SQLCrazyCertified (5/3/2012)
Gazareth (5/3/2012)
I'm trying to work this out as well.I can understand the problem with a production outage if the DR site goes offline, but if the mirror's at the principle location and that site goes offline, then you won't get automatic failover?
I believe if you have the witness server and principal server in the same location and if there is a power outage, then mirror server will become the principal server......correct me if I am wrong....but if the mirror server cannot communicate to witness server/principal.....it should fail over automatically right?........then you need to manually script out the logins, alerts, jobs etc....at the mirror server.
No, the mirror needs to be connected to the witness before it can recover to operational status & assume the role of principle.
Need a quorum of at least 2 of the 3 servers before anything can happen.
Cheers
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