Azure SQL Database

Question

Folks,
Not sure if this is the right forum to ask these questions, I am planning to sign up for Azure SQL Database and VMs. I am trying answers to following. Any information is appreciated.
What is the reliability measure of the Azure SQL Database. Is it five 9’s ?
What is the "MAX Worker Threads” performance measure as mentioned here:
http://msdn.microsoft.com/en-us/library/azure/dn741336.aspx
Does “MAX session” correspond to maximum number simultaneous of DB JDBC connections.
Is it tenant based service where multiple tenants are hosted on the Azure database.
What is the architecture of Azure SQL database, Is it centralized on a single server or over a cluster of machines ?
What is the high level architecture of the VMs and SQL DB.
What is the nature, bandwidth and reliability of connectivity between Azure VMs and Azure SQL DB.
Is this network capacity between VMs and SQL DB shared between multiple tenants.
How are the SLAs guaranteed (ensured) and throttled/enforced (to curb over-utilization).
If we horizontly scale Azure VMs to twice number of current VMs, will the temporal locality of the new VMs has lower network performance in terms of latency or bandwidth than the existing VMs.
Are there any per Azure VM limits on access to Azure SQL DB.
If for some reason SQL DB crashes experiences, Is the Data recoverable.
Can the Azure SQL DB be backed up in Azure Cloud/ or Amazon S3
Thanks,
Ajay

Answer 1

Hi Ajay,
These msdn forums are the actually the best place to ask questions. 
I guess you have some scenario in back of your mind that makes you ask these questions, if you can share that with us we may better answer your questions instead of giving you information that may not be most usable for you, regardless here it goes.
I will do my best to answer all your questions
What is the reliability measure of the Azure SQL Database. Is it five 9’s ?
VS: It's 4 nines (99.99) The 99.99% uptime SLA applies to Basic, Standard, and Premium service tiers only. 
SQL Database Web and Business Editions have an established uptime SLA of 99.9%.
http://azure.microsoft.com/en-us/services/sql-database/
What is the "MAX Worker Threads” performance measure as mentioned here:
http://msdn.microsoft.com/en-us/library/azure/dn741336.aspx
VS: SQL Database governs the limit on the number of concurrent worker threads (requests) to a database. 
Any database with more than the allowed limit of concurrent requests will receive error 10928, and further requests on this database can be denied.
http://msdn.microsoft.com/en-us/library/azure/dn338078.aspx
Does “MAX session” correspond to maximum number simultaneous of DB JDBC connections.
VS: Yes, SQL Database governs the limit on the number of concurrent sessions that can be established to a database. When concurrent session limit for a database is reached, new connections to the database are denied and user will receive error
code 10928. However, the existing sessions to the database are not terminated.
http://msdn.microsoft.com/en-us/library/azure/dn338078.aspx
Is it tenant based service where multiple tenants are hosted on the Azure database.
VS: Yes and No, Yes because its offered as SAAS, yes multiple tenants are hosted on Azure DB, but they are isolated and also depends on the tier you choose. SQL Azure is designed for Massive scaling, so if you were worried about slowness due
to multi tenant hosting, trust me that should last thing to be worried about.
No, because you can choose to go all the way to premium (now that does not mean you are the only db on the server but its super high performing database out there)
What is the architecture of Azure SQL database, Is it centralized on a single server or over a cluster of machines ?
VS: Its hosted in Microsoft Datacenters and offered as a service, although we can go in detail of architecture of SQL Azure but for this set of questions its irrelevant. Performance is massive on SQL Azure, it can be scaled out or scaled down
on demand.
What is the high level architecture of the VMs and SQL DB.
VS: Not following your question here, what is meant by architecture of VM?
What is the nature, bandwidth and reliability of connectivity between Azure VMs and Azure SQL DB.
VS: The connectivity in general is great unless you decide to host one service in part of the world and other totally other corner, in that case also I have seen good connectivity between the two given normal latency.
Is this network capacity between VMs and SQL DB shared between multiple tenants.
VS: Not following your question in entirty, do you mean network capacity in terms of GB/Sec? if your vm and sql are in same Data Center its the fastest connectivity you can get out there in market on any cloud or for that matter on prem :)
they apparantely have a faster network in their DC than many giant companies have on prem.
How are the SLAs guaranteed (ensured) and throttled/enforced (to curb over-utilization).
VS: MS have protection against many threats, DOS being one of them, Microsoft has done the best job among all the cloud providers out there to inform thier customers about outages, in a recent summit this was also discussed in detail and suggestions
were made to improve on the portal feature.
Each time an service goes down its reported on the portal on service health page, they are improving on the SLA breach report, at this moment its part of your invoice. I have personally not seen a single breach on my services, I am actively using Azure for
last 5+ years.
If we horizontly scale Azure VMs to twice number of current VMs, will the temporal locality of the new VMs has lower network performance in terms of latency or bandwidth than the existing VMs.
VS: number of VMs have nothing to do with network performance, keep in mind the fabric underneath is build for massive scale, network performance and latency will vary (they keep improving) if you choose to create your VMs in a different DCs
then you would come across some latency and that's normal. 
Are there any per Azure VM limits on access to Azure SQL DB.
VS: these are not per VM limits, they are driven by MAx_THREAD and MAX_SESSION, please refer to the link above in the question for Max worker thread
If for some reason SQL DB crashes experiences, Is the Data recoverable.
VS: I would be careful to answer this, if you choose to use SQL Azure (which is offered as SAAS) then yes MS takes care of data replication to ensure SLA. if you choose to host your own SQL DB on your VM in Azure, MS is not responsible for
the data recovery, you will have to take care of it (because now you are not talking about PAAS, instead you are going for IAAS)
Can the Azure SQL DB be backed up in Azure Cloud/ or Amazon S3
VS: Ofcourse, I am not very familiar with Amazon S3 but i see no reason why it can't be done.
hope this helps
Please mark as answered if it helped
Vishal Narayan Saxena http://twitter.com/vishalishere http://www.ogleogle.com/vishal/