Mirroring a server

[Charles Steinkuehler]

jcrowe at cmuonline.net wrote:

> On Tue, Jan 27, 2004 at 10:44:57AM -0600, Charles Steinkuehler wrote:
>> ...and put some serious thought into exactly *HOW* available you really 
>> your system to be.  Is a nightly rsync good enough?  Do you really need 
>> fully transparent failover, and if so, do you have the budget (not only 
>> in $ but in install/configuration/maintainence man-hours & knowledge) to 
>> implement it?
>> 
> I don't really need automatic failover (I don't really want it either). I guess I will use rsync 
to keep them up to date. What kind of hit am i gonna take if i run rsync every 15 minutes or half 
hour?

It depends on how much has changed, but rsync is *VERY* good at syncing 
large amounts of data in a very short time, and you can always 'nice' 
the rsync command if it starts eating too much CPU.

As a point of reference, I can re-sync my local copy of the debain 
mirror (no changed files) in 3 minutes across a 384KBit/s link:

-bash-2.05b$ time bin/sync-debian
real    0m48.850s
user    0m1.960s
sys     0m1.090s

The nightly syncs take 1-2 hours, depending on how much changed in 
unstable that day, since I have so little bandwidth.

My local archive is 23G (I only mirror the i386 and alpha binaries), and 
consists of 42796 files:

-bash-2.05b$ du -hs data/debian
23G     data/debian
-bash-2.05b$ find data/debian -type f | wc -l
   42796

With 100 MBit or 1 GBit ethernet, rsync should work very well for your 
purposes.  You'll want to be careful with any open files that are 
important to rsync correctly (like open databases), and setup something 
to make sure these files are handled correctly.

-- 
Charles Steinkuehler
charles at steinkuehler.net