One of the biggest questions that I get from customers is about backups.\u00a0 Systems are built on data, and data lives on storage media (usually hard disk drives), and storage media has a known failure rate.\u00a0 It’s a known fact that storage media fails, and when it fails, bad things happen. It’s important to differentiate between system and media failures (which are components that just go bad) and Disasters (which are things that happen to your business, such as tornadoes or acts of god, that are independent of single failures).\u00a0 Disaster Recovery is a whole separate topic, which I will cover at a later date, which is equally important. But now back to\u00a0system backups…<\/p>\n
I learned the hard way, a long time ago, with an ancient Mac laptop and school work.\u00a0 Disk failures happen, and when they do, you’re screwed unless you have backups.<\/p>\n
This leads to the rule: always have 2 copies of your data.\u00a0 One of live data, and another of a\u00a0recent backup.\u00a0 How recent? There is the question.\u00a0 How much data can you recover from reentering transactions and\/or manual recreations of entries that you’ve already done?\u00a0 If it’s a few dozen, then probably not a big deal.\u00a0 A few thousand, then it’s not so easy.<\/p>\n
This leads to the first term in backups: Recovery Point Objective (RPO).\u00a0 RPO is how long you can stand to manually recreate transactions that have already happened.\u00a0 If your RPO is 4 hours, then you only expect to have to re-create 4 hours of transactions after a data restore after a failure.<\/p>\n
The other consideration for backups is Recovery Time Objective (RTO), or “how long does it take to restore the system to the RPO”.\u00a0 After a failure, how long does it take to obtain the backups, obtain restore media, and do the restoration? Data Restoration typically takes hours, and sometimes longer, so RTO is an important consideration.\u00a0 If a short RTO is required, then a system that stores duplicate data is usually warranted.\u00a0 You replace failed storage A with backup storage B, and you’re done.\u00a0 Quick, but expensive.\u00a0 If you can stand a longer recovery time, then you live with a backup drive that takes minutes or hours to restore to other media. While the restoration is in progress, the systems are off line and nothing is happening.\u00a0 After the restoration, the system still has to be recovered with the non-backed up transactions.\u00a0 Therefore, the true recovery time will be: time to detect the failure + time to restore the backup + time to reenter the transactions since the backup.\u00a0 That could be hours or days. How long can you be in limbo?<\/p>\n
There’s a serious cost-vs-time tradeoff for backups.\u00a0 Rest assured, 10 out of 10 systems will fail.\u00a0 The question is when.\u00a0 Are you prepared?