On Mon, 26 Jan 2004 [EMAIL PROTECTED] wrote: > I was talking about our backup strategy to my wife tonight (2 sets of > full backups, nightly incremental backups onto CDRW: again, 2 CDs that > we cycle between), and we started discussing what seems to be a huge > hole in this common strategy. > > Namely, if you damage or lose any file you've worked on since the last > full backup, and don't notice within two days, then the work will be > lost - wiped out by the nightly incrementals! > > This likelihood obviously increases as the length of time between full > backups increases. E.g. for us, we only fill an incremental CD a few > times a year, so we only do a few full backups in a year. > > What's the accepted practice for solving this problem? I thought of > keeping a 3rd CDRW for the incrementals, that only gets pulled out and > used say on the 1st of each month. At least then you have a month to > realise you have some damaged or lost files. ANd you could I suppose > extend this to have 2-monthly, 4-monthly media you used, and have some > complex scheme for pushing and popping them, so that for N media, you > could be safe for 2^N months. But that seems complex.
You either live with the data loss possibility, or you make modifications. We use a "grandfather Father Son" method which runs something like this. Monday - start of week - differential backup - no clear of archive bit Tuesday - differential backup - no clear of archive bit Wednesday - differential backup - no clear of archive bit Thursday - differential backup - no clear of archive bit Friday - full backup - archive bit cleared. The difference between a differential backup and an incremental is that the differential does NOT clear the archive bit - so on Mondaym you get files changed over the weekend plus Monday, Tuesday you get all that again plus files changed Tuesday etc etc. The daily tapes get reused each week - which gives a full 7 days for someone to notice a lost file - and the end of week get reused every 6 weeks or so, with a monthly tape make at the end of each month and kept for a year. However, there's still the possibility of data loss - but it's much smaller. A file created on, say, Tuesday, and deleted on Wednesday can still be recovered until the next Thursday - but after that it's gone. You need to make a call balancing the possibility of data loss against media cost - since you're only backing up to CDRW, buy a couple of dozen and cycle them in a two or three week cycle - only save the incremental data to ONE disk, then save that disk for two or three weeks. More complex, but less chance of something going missing. It all comes down to what you weant to spend. The way to minimise the chance of data loss best is to do a full backup, every day, and never recycle media - but this gets _damn_ expensive! DaZZa -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
