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briankind
Starting Member
17 Posts |
 Posted - 2009-07-25 : 10:34:54
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| what is high availablity ? dont we just schedule full back ups on saturdays when there are no production? |
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webfred
Master Smack Fu Yak Hacker
8781 Posts |
Posted - 2009-07-25 : 14:39:31
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There are organisations that need the system 7 days a week and 24 hours a day.They cannot live with a longer downtime because of a hard disk crash or something.High availability is something like this:There is a production (SQL) Server.Applications are connected to this server.This server is known as PRINCIPAL.There is a mirror (SQL) Server.Mirroring is done from PRINCIPAL to MIRROR.So MIRROR always is up to date like PRINCIPAL.There can be a third server as WHITNESS to control the system.In case of a problem with the PRINCIPAL a failover happens to the MIRRORNow the MIRROR is the PRINCIPAL and the applications can go on with their work.And so there is time to repair that one server without having a long downtime.
No, you're never too old to Yak'n'Roll if you're too young to die. |
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SwePeso
Patron Saint of Lost Yaks
30421 Posts |
Posted - 2009-07-25 : 15:28:39
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For two years ago, I helped out with some code for an online betting site.It was really interesting to hear about their environment."Now we're talking 24x7x366"If I remember correctly, they calculated their loss of revenue per minute of availability downtime, in millions...
N 56°04'39.26"E 12°55'05.63" |
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GilaMonster
Master Smack Fu Yak Hacker
4507 Posts |
Posted - 2009-07-25 : 15:56:35
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| I used to work for an investment bank. The main trading system had to be available all the time during the workingday and there was absolutely no data loss allowed.Say we only had full backups on saturdays and nothing else and we had a disaster on the thursday. This was a 1TB database that could take over an hour to restore. Firstly, having the system down for an hour to restore would have lost the bank tens of millions of dollars. Losing all the data for half a week of trading would virtually put us out of business.Some things to be aware of. High availability is not the same as backups and backups are not a form of high availability. http://sqlinthewild.co.za/index.php/2009/05/08/high-availability-backups/High availability is the ability of a system (not a server) to be available to users no matter what disaster happens, from a power supply failure to a hard drive failure to a full server failure to the loss of an entire data center (hurricane, meteor, earthquake). Now you may chose not to handle some of those (redundant data centers are expensive), but it depends on the degree of risk and the potential loss. If you're talking a small system used in Joe's corner shop to track sales, maybe it doesn't need any form of high availability. When you're talking about banks or Peter's betting company, they need really expensive, really well planned out HA systems.Database mirroring, which is what Webfred was talking about, is not the only form of high availability. It's one form, there are many others. There's no one that's best, it depends on what you're doing, what kind of availability you need and how much you're willing to spend on it.Backups are there to allow you to recover from a disaster, but they are not going to help a system to remain available despite a disaster.--Gail ShawSQL Server MVP |
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GilaMonster
Master Smack Fu Yak Hacker
4507 Posts |
Posted - 2009-07-25 : 15:58:59
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| Brian, you're asking a whole lot of fairly introductory level questions. Are you a developer just getting into SQL? Have you been thrown into the DBA role and are trying to get to grips with it? Are you just interested in SQL?There's a lot of good articles, blogs, books and resources I could possibly suggest, but would like to know what your situation is first .--Gail ShawSQL Server MVP |
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what is high availablity ?