Voice of the DBA

Tag: syndicated

  • RTO in Disaster Recovery

    When you have a disaster, the time that you have to restore service is usually referred to as the RTO time. This stands for the Recovery Time Objective and it can is defined like this in Wikipedia:

    The Recovery Time Objective (RTO) is the duration of time and a service level within which a business process must be restored after a disaster (or disruption) in order to avoid unacceptable consequences associated with a break in business continuity.

    That’s a great definition, covering the term with a great set of large, geeky words. However I came up with a simpler one that conveys the same information:

    The time it takes for you to get things running to the point where someone can use them after someone notices that they aren’t.

    You can also view the RTO as the downtime or uptime level of your system. I prefer looking at the RTO as the intervals between uptime, since I think that’s a glass half full view.

    That’s the basic definition and it’s important that you determine what the RTO is for your systems in order to begin planning for the resources that you devote to disaster recovery preparation.

    This post is based on the information in my Preparation for Disaster talk.

  • How Should We Pay People?

    It’s an interesting article on how to pay people from Dan Ariely at Business Week. It’s a look at some of the issues with paying for knowledge work, or work that isn’t well defined. The short version is that you don’t want to specify too tightly what you expect people to do, but then you have to motivate them to work in the best interests of the company.

    I think this is one of the fundamental problems in management today. We still have this mentality from the blue collar factory worker and piecemeal or easily measurable work items being applied by management to knowledge workers. It doesn’t work well, and somehow we think that the hours work in some way relate to the output.

    I blame lawyers. They tend to use this model, since they often bill by the hour. However the end result, the quality of that they produce, which is usually research, isn’t easily quantified in anything other than a win or loss. That often comes down to not only the soundness of the argument or the logic, but the charisma of the lawyer. That’s not even close to the way we do business in many other industries, especially technology.

  • Recovery Models

    In SQL Server we have three basic recovery models: full, bulk-logged, and simple. By default we find that most databases use the defaults, which mean that they are in the full recovery model.

    In that case, you need to be sure that you are performing log backups, otherwise the log will grow until it reaches it’s limits, or you run out of disk space on that drive. If the log cannot record SQL Server transactions, the database cannot accept any more transactions.

    The basics of recovery models are covered nicely in this article from Gail Shaw, which includes some common myths and misconceptions out there. However for the average person, the important thing is that you understand which recovery model to pick.

    You Need Point in Time Recovery

    Point in time recovery means recovery in between the full or differential backups. Quite a few DBAs will ask customers if they really need to recover to a point in time, and get the answer that they don’t, but that’s not often the right question to ask.

    Ask your clients if the database failed at 5:00pm today, and all the work done today was lost because you restored to last night’s backup at midnight, how would they feel?

    Sometimes they’re fine with the data loss, most times they aren’t. If you need to get back to a point in time between backups, make sure you use the full recovery model.

    You Can Reload the Database

    There are some databases, usually data warehouses, that can be rebuilt from other sources. If you take a backup of your database and then load data every day that rarely changes during the day, you might not need point in time recovery. In fact, many ETL processes are not designed for this anyway, and could not restart themselves in the middle of a load if you restored to the point in time when the database had an issue.

    In this case, use the Simple recovery model.

    You are space constrained with the log

    If you run index rebuilds, or large data loads and find yourself with a transaction log that grows very large, you might want to investigate the Bulk-logged recovery model. This model is more confusing, so I don’t want to give you a general rule here. If you think you might benefit from less logging, investigate the bulk-logged recovery model, practice restores with it and make sure you fully understand the implications of using it before you set a database in this mode.

  • Prepping for Certification

    Having prepped for, taken, and then failed the MCM exam this year, perhaps I’m not the best person to give you advice for certification preparation. However the MCM is a hard test, I did better than I expected, and I was close. Lots of people haven’t passed it on their first try, including a couple people that work with SQL Server every day to build solutions that must work in the real world. A few of them passed on their second try, though I’m not sure if I’ll take it again anytime soon.

    Recently I ran across this preparation post from Susan Ibach on MSDN. I think it’s good advice and if you follow it, you’ll be prepared for the exam. At least you’ll have a good idea on which general areas the exams focus on since there are %s given for each area. I’ve shown part of the SQL Server exam 70-450:

    cert1

    Note that this section, which includes security for the instance, database, schema, and encryption, is 15%. Since the exam is supposed to be around 50-60 questions, this means that you should get about 10 questions on security. You might get 8, you might get 12, but I wouldn’t expect to get 20.

    I know most of you would like a step by step list of things to do for the exam. However these exams are going to test a wide variety of skills, and since 50 questions isn’t a lot, the exam can’t specify tightly which questions will be asked.

    Sidebar: Personally I’d like to see more specific exams, perhaps as specific as security, replication, SSIS, etc., but lots of people don’t want to certify in all those areas. Plus it changes the profits for MS since they have more exams to administer. We’ll see if this changes in the future.

    As a result you need to study a wide variety of materials. For example, for the security section above, you ought to tackle this in 5 sessions. Build yourself a short list of skills to have in each area. I’ll do section one for you. Here is what I’d go read about in BOL and practice in SSMS.

    If you can explain each of these things to someone else, and perform the skills, you should be fine. I would recommend you blog or write about these, because that helps you to learn and remember this stuff. If you blog about them, ask a friend to look at your blog and see if you have correctly described things.

    Once you think you’re OK with all the sections, not perfect and a guru, but you understand these areas, take the exam. If you want extra practice, get a MeasureUp or other practice test.

    There’s no guarantee and you shouldn’t expect one. Go through the material, explain it back to yourself or someone else and you should be able to pass the test.