Re: Backup solutions.

On Mon, Jun 04, 2007 at 05:23:11PM -0600, Lance Levsen wrote:
> I guess this is two-fold. My real question is, am I paranoid enough? :)

It's basically an exercise of risk assessment and managment.

The big thing here is to try and quantify the value of your data. If it's
lost, what is the cost. Some data may be worth more than other data (e.g.
accounts receivable data is probably more valuable than a library of
downloaded software which can be easily replaced). Also factor in partial
data loss (eg the data lost between backups) and downtime.

Now, look at the probability of losing the data. If you dig around on the
net, you should be able to come up with some data to compute the chance of
a failure for your primary storage.

To calculate your exposure, multiply the probability of failure by the value
or cost of the data. Your backup solution should not cost more than this.
Adding a backup solution will reduce your exposure since the backup reduces
the risk of data loss. Also consider insurance, it may be cheaper to just
do a basic daily backup on DAT tape and pay for insurance against the
building blowing up or whatever disaster may happen. Of course, it may be
better to use an off-site remote, live backup solution.

> Obviously there are constraints. The data is more important than
> continuous uptime, so we choose to have a system go down for half a day
> replacing a store-bought drive from backup rather then relying on RAID
> for drive failure contingency.

This tells me you've thought about this a bit. If downtime is not expensive
and assuming you can afford to lose a day of data, nightly backup and a
plain (non-RAID) drive is probably good enough.

At work, I do daily differentials and a weekly full backup on a 6 week
cycle to near-line storage for most data. More important data is also
shipped off to tape (2 copies, one off site and one on site).

On my linode, I just do the daily differential to my server at home. I run a
full backup only if I make significant changes to the system. I only keep
the last few differentials around. On my home systems, critical stuff is
copied to another disc spindle in the same box.
Received on Mon Jun 4 18:44:08 2007