Mirroring
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Our database servers are located at our ISPs datacenters. They 'own' the hardware.
They have 2 datacenters widely separated. We mirror the databases from one to the other. We run in asynchronous mode with no witness.
The databases are backends for public websites.
Over the last few months we are seeing many connection issues on the mirror.
On investigation we see that the database servers only have one NIC. All the traffic, public client and mirror, goes over this single NIC.
I submit this is *bad practice*
I would prefer to see a sparate NIC dedicated to the mirror traffic.
I'd like some opinions. Am I correct? The databases vary in transaction rates from 10 per day to millions per day.
DBA (Dogsbody with Bad Attitude)
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I would start by asking your ISP how they handle network access/load balancing.
Most probably what you are seeing as a NIC is a virtual-NIC masking an underlying load balancing structure.
Is it mirror supposed to be accessed all the time or just in case primary site goes down?
_____________________________________
Pablo (Paul) BerzukovAuthor of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice. -
I have some more info, and this is the reason I HATE not having control of the hardware.
The servers are physical boxes, not virtuals.
There is indeed, only one NIC in the server (!?) and ALL the traffic goes over a 1Gb link between the datacenters.
Thats is public traffic and admin traffic and DR mirros and replication traffic.. everything.
We were sold this as a DR solution.. right now we're seeing less than 1 Mbit/s in the mirroring monitor while the mirror tries to resync.
Time too look for another ISP I think.
DBA (Dogsbody with Bad Attitude)
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Sorry, I didn't actually answer your question there did I.
Yes, theres a load balancer, but only the web servers are on it.
The mirror is only accessed during a failover.
The principle is a cluster with 2-nodes, both active with a shared SAN resource. Some databases are on one node some on the other. (I didn't set this up, by the way, it's inherited)
The mirror is set up the same way.
DBA (Dogsbody with Bad Attitude)
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Barry G Freeman (5/25/2010)Time too look for another ISP I think.
I would start by taking a look at the contract...
-- Are there any SLAs?
-- Is ISP meeting SLAs?
-- Are there penalties if SLAs are not met?
-- Is ISP responsive?
May be the architected solution was good time ago but it is not good today... did the application grew in terms of either traffic or data storage?
Described solution looks like a managed hosting service, may be it is time to go colocation and have total control of your hardware - which will come along with the responsibility of keeping the platform in working condition and the capital expenditure and related costs of owning it.
_____________________________________
Pablo (Paul) BerzukovAuthor of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice. -
Something is very wrong here.. I'm starting to supect something as simple as a dodge network card.
We're now seeing this
Notice the per-second droputs and lousy transfer rate - this is supposed to be a 1Gb link
DBA (Dogsbody with Bad Attitude)
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I'm trying to get hold of SLA's and so forth, and yes the ISP is responsive - their suggestion was we go to log Shipping instead of mirroring.
DBA (Dogsbody with Bad Attitude)
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Barry G Freeman (5/25/2010)
Notice the per-second droputs and lousy transfer rate - this is supposed to be a 1Gb linkDid the ISP promised a private 1GB link or did they say they have a 1GB link in between sites?
Second version may imply 1GB link is shared by all customers.
_____________________________________
Pablo (Paul) BerzukovAuthor of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice. -
Well, I'll need to get hold of the original contracts, but I'm thinking that they never specified a private link of any sort.
As with all inherited systems, I'm finding it really difficult to find out things, and it's all too easy to blame the contractors who originally set this up.
Lets assume that this is a single shared pipe. Even with that proviso, we're still only seeing 1Mbit/s which to me, seems awfully low.
It may well be that we will have to go to log shipping. I will make sure that every server involved has SQL Backup on it though.
DBA (Dogsbody with Bad Attitude)
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Barry G Freeman (5/27/2010)
As with all inherited systems, I'm finding it really difficult to find out things, and it's all too easy to blame the contractors who originally set this up.Believe me, I feel your pain and I agree there is no point in blaming whoever was before in charge.
The idea is to figure it out what is the ISP supposed to provide - that's why I insist in looking for the contract, then focus in solving the problem.
Imagine this scenario... you have a contract where ISP agreed on a SLA of 1 Gigabit; first attempt of solving the current issue will be to ask ISP to keep its contractual obligation.
Now... imagine this other scenario... contract with ISP has no SLA at all and states service will be provided in a best-effort basis; in this case you know you are on your own and have to either negotiate something better with the ISP, figure it out how to keep your infrastructure running with whatever you are getting or consider moving to a different provider/solution.
Starting point is to know what kind of service and what kind of quality of service you are supposed to be getting. 🙂
_____________________________________
Pablo (Paul) BerzukovAuthor of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
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