2010/11/22 Kshitiz kshitij_kotak@hotmail.com:
I feel a full backup once in 400 days, with hourly incremental, daily incremental and weekly incremental backup being rotated in a way in which 1 full backup followed by 24 hourly incremental backups, interspersed with 7 daily incremental backups and 5 weekly incremental backups may be protection enough for my data. What is the you all's expert opinion?
I am assuming you meant 40 days, and not 400 days. :-)
Let us say a full backup takes 30 minutes to restore, each weekly incremental takes 5 minutes to apply and each daily incremental, 1 minute. Let us further say you have an outage 33 days after your previous full backup. Now, the time for you to restore is:
30 minutes to restore the last full backup 4 x 5 = 20 minutes to apply the 4 weekly incrementals since the last full backup 5 x 1 = 5 minutes to apply the 5 daily incrementals since the last weekly incremental
Total time taken to restore = 55 minutes ~= 1 hour.
Now, nobody else apart from you can say whether 1 hour of downtime while you restore from backups is acceptable or not. The right way to design your backup schedule is to first determine what the acceptable limit on this time taken to restore (called MTTR, or Mean Time To Recover - a little bit of statistics enter here to determine this "mean") is, and then work backwards. You will find that your entire backup strategy can change with your acceptable MTTR.
A second issue you haven't addressed is that the smallest incremental you have is hourly. So then what happens if an outage occurs 55 minutes after the last hourly incremental? Are you fine with losing 55 minutes worth of data?
Binand