This, unsurprisingly, puts pressure on backup resources, hardware requirements and data growth management \u2013 pressure that may actually be totally unnecessary. In short: if you do your full backups on the weekend because “that’s the way it’s always been done” then you might want to stop and consider the alternative.<\/p>\n
Let’s take a sample small business, and map out their weekly backup cycle. This isn’t actually one of my customers, but it is an average of several of them:<\/p>\n
- \n
- Monday \u2013 150 GB backup.<\/li>\n
- Tuesday \u2013 203 GB backup.<\/li>\n
- Wednesday \u2013 168 GB backup.<\/li>\n
- Thursday \u2013 317 GB backup.<\/li>\n
- Friday \u2013 2114 GB backup.<\/li>\n
- Saturday \u2013 3619 GB backup.<\/li>\n
- Sunday \u2013 744 GB backup.<\/li>\n<\/ul>\n
If you’re doing a basic weekly backup cycle in a small to medium company then this sort of minimum, maximum and peak loading probably looks awfully familiar.<\/p>\n
Graphing this out, we get an interesting view of the backup size peaks and troughs:<\/p>\n
![\"GB](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2011\/02\/GB-backup-nonsmoothed.png\" "\\"GB")
<\/a><\/p>\n“Streuth!”, an ocker Australian would say, “That’s a bloody big difference in backup sizes!”<\/p>\n
In fact, if we look at those backup sizes on a comparative pie chart, we get the following:<\/p>\n
![\"GB](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2011\/02\/GB-backup-nonsmoothed-pie.png\" "\\"GB")
<\/a>Viewed this way, the weekend backups take up a significant percentage of the overall backup activity \u2013 which means they become a dominating factor in determining an optimum backup environment size. In fact, it shows us that 88% of the total amount of data backed up in a week is backed up in just 43% of the week – 3 out of the 7 days. The remaining 12% of data backed up during the week places no pressure on the backup environment at all.<\/p>\nIf we come up with an average backup speed \u2013 let’s say 50MB\/s for a smaller environment \u2013 we can see how long, in average terms, each day’s backup takes:<\/p>\n
![\"Hours](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2011\/02\/hours-to-backup-nonsmoothed.png\" "\\"Hours")
<\/a>Ouch \u2013 our system barely needs to tick over Monday through to Thursday, but once the weekend hits, it’s really having to work hard to get everything backed up.<\/p>\nThe net result? Backup windows may be regularly overrun, and even a moderate amount of data growth may necessitate new capital investment.<\/p>\n
Or will it? Let’s instead consider the same amount of data backed up, but with full backups spread out over the entire week. Now, admittedly here I’m not averaging numbers, but spreading sizes pseudo-randomly out over the week to match the previous amount of data specified. So our numbers instead look like:<\/p>\n
- \n
- Monday \u2013 983 GB<\/li>\n
- Tuesday \u2013 733 GB<\/li>\n
- Wednesday \u2013 842 GB<\/li>\n
- Thursday \u2013 928 GB<\/li>\n
- Friday \u2013 1357 GB<\/li>\n
- Saturday \u2013 1536 GB<\/li>\n
- Sunday \u2013 986 GB<\/li>\n<\/ul>\n
[Edit: Qualification – an anonymous reader here questioned whether I meant doing a full backup every day. I didn’t quite explain my thinking here, sorry. I mean spreading out the full backups so that instead of trying to do them all over a short period, they’re spread out over the week. E.g., instead of every server doing a full backup on the weekend, some would do full backups on Monday, some on Tuesday, some on Wednesday, etc.]<\/em><\/p>\n
If we graph that, using the same minimum\/maximum as before, the spreading of full backups has smoothed the daily backup sizes considerably:<\/p>\n
![\"GB](\"https:\/\/nsrd.info\/blog\/wp-content\/uploads\/2011\/02\/GB-backup-smoothed.png\" "\\"GB")
<\/a><\/p>\nMoving on to a pie graph, we can see that no single day dominates like before:<\/p>\n