Like clustering, database mirroring can provide seamless
failover (you must configure it to do so). Like log shipping, it maintains two separate
copies of the database. Like clustering but unlike log shipping, database mirroring can
(again, there??™s a catch) have no more data loss than a single incomplete transaction. And
like log shipping but unlike clustering, there is technically no limit to the distance
195
C H A P T E R 8
between the two copies of the database. Theoretically, you could have a database in
Chicago that maintains a mirror of itself in Shanghai. Does it sound too good to be true?
Once you take a closer look at the architecture, you??™ll see that the plumbing
behind the conceptual architecture unveils a wealth of moving cogs. It isn??™t as simple
as being managed by a specific service (clustering) or as basic as automating standard
activities such as backing up and restoring transaction logs. Database mirroring is
deceptively complex and has a number of dependencies that you must consider when
implementing it.
The Basics
Taking a cursory look at database mirroring, as shown in Figure 8-1, you??™ll see that the
architecture looks a lot like log shipping.
Pages:
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378