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Oracle RAC is using shared-disk architecture. I cant see why this can make the whole product highly scalable or available ? the shared storage can itself turn into a single point of failure. and if we are using for example SAN for our storage, we are as scalable as the SAN controller and we will need to replicate our data into other SANs or another lun in our current SAN. Its like we are using storage for every replica in isolation and its kind of like shared-nothing architecture in which we gather all of our data in one place physically. what is the benefit of sharing here?

Armin Balalaie
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    This question is being voted for closure because the author does not show a level of technical understanding or appropriate due diligence in researching the topic that the community judges as being a minimum barrier to participate. – Wesley Mar 06 '15 at 16:49
  • Oracle RAC is concerned with making Oracle components highly available. It's not concerned with how you make your shared storage, or any other infrastructure component, highly available. It's not the responsibility of Oracle RAC, or any other product, to take into account and provide an HA solution for your entire IT infrastructure. – joeqwerty Mar 06 '15 at 19:45

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They need shared storage because in order to allow multiple servers to handle to load - including in the event of losing a whole server - they all need to be able to access the same data. Yes this can be a single point of failure but you design around this by ensuring that your storage has multiple controllers/PSU, control-paths, appropriate RAID levels, and data access paths - you can even locally-or-remotely cluster your storage. This way this 'single point of failure' actually becomes one of the MOST reliable parts of the design, allowing you to simply throw as many DB servers at the problem as you need.

This isn't just a smart way of dealing with transactional data by large organisations - it's the ONLY way!

Chopper3
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  • but you are ignoring the IO bottleneck of the underlying disks, the controller capacity to handle the requests, the write lock manager and etc. These are the limiting factors that prevent us from linearly scaling out, even for read-heavy workloads. – Armin Balalaie Mar 06 '15 at 16:22
  • You said "They need shared storage because in order to allow multiple servers to handle to load - including in the event of losing a whole server - they all need to be able to access the same data" we can achieve this using a shared-nothing architecture either. what is the point of sharing? – Armin Balalaie Mar 06 '15 at 16:24
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    No I'm not - we use RAC extensively and our SAN arrays have *FAR* more disk bandwidth and IOPS available to them than anything you could directly attach to a single server - same goes for the controllers - WAY more ports and performance than any DAS controller and the locking is done by ASM and scales out to tens of servers. Look let's agree to disagree - there are some applications that 100% NEED to use shared data and some that don't - we use Splunk heavily and that doesn't need shared data. Perhaps if you worked in a larger environment you'd have seen the need for shared storage. – Chopper3 Mar 06 '15 at 16:30
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    Ah and I've just spotted - as we make very clear on this site when you sign up this is for IT professionals - it's not a 'learning site' for beginners - and this is a homework question, as is your other question - we're not here to do your work for you but good luck with your studies ok ;) – Chopper3 Mar 06 '15 at 16:37
  • Please show some respect :). I am not a beginner. A beginner won't ask questions like this! He will ask about SQL! I am a researcher and trying to find out which DBMS solutions will better suit your needs during migration to the cloud. if you dont want to help no one can force you. Anyway i dont want to compare san to das. I just want to know why sharing is beneficial for scalability? why we cant have scalability without sharing e.g. using distributed database? it this about relations and complex queries? – Armin Balalaie Mar 06 '15 at 16:45
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    `I am not a beginner. A beginner won't ask questions like this!` A beginner will think that a beginner won't ask questions like this. – Wesley Mar 06 '15 at 16:48
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    @ArminBalalaie Two things: Your question and responses are very amateurish, whether you're a student or not. Secondly, Chopper3 is one of the most widely respected members here due to his experience, knowledge and the amount he's helped over the years and I suggest you wind your neck in. He even answered your question and clarifications for you. – Dan Mar 06 '15 at 16:49
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    Firstly you *are* a beginner, you're a student/researcher, seemingly a smart and well-read one but presumably you've never been paid to build out production quality systems? secondly show *US* some respect by adhering to our site guide, which states that this isn't a learning site - that said I was trying to help you. I'm a designer for some of the largest IT systems ever created and your views on databases are very 'black and white', whereas seasoned professionals have to be open to all manner of options based on actual experience. – Chopper3 Mar 06 '15 at 16:50
  • I am really sorry. maybe my English is impolite. Forgive me if I cant say my words politely. English is not my first language. and I am really thankful that you are responding to my question dear @Chopper3 – Armin Balalaie Mar 06 '15 at 16:52
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    Don't worry, your English is WAY better than my Iranian - I'm a huge fan of your country, history and people by the way, I have lots of Iranian friends and colleagues. I just wanted you to understand that this site is about the practicalities of making real stuff work in a professional environment, I suspect you need to find somewhere that's more suited to discussing theoretical or design-based systems - have you seen http://dba.stackexchange.com/ ? – Chopper3 Mar 06 '15 at 16:56
  • thank you for nice words about Iran. I am really sorry if I made you angry. Can I have an email from you and ask some questions privately? or have an interview if you have time ... you look pretty experienced :) – Armin Balalaie Mar 06 '15 at 17:10
  • You didn't make me angry - just wanted you to be clear about the purpose of this site is all, lots of other people do the same, don't worry. And I already have to do quite a lot of PR/public-speaking/educational stuff and I'm just getting over being a bit ill so I can't help right now, perhaps ask again in a short while? – Chopper3 Mar 06 '15 at 19:22
  • ok. but how can I get in touch with you? that would be great if you provide me an email address so I can ask you later. my email is armin.balalaie [at] gmail [dot] com. can you please send me an email? :) – Armin Balalaie Mar 06 '15 at 20:08