backup & low downtime for home network

[Lennart Sorensen]

On Wed, Dec 05, 2007 at 03:11:46PM -0500, Chris Aitken wrote:
> I want to have a backup system for our home network. We have four PCs 
> (I'm going to call them PCs here to mean they are linux computers as 
> opposed to MACs - I don't mean PC as in a Microsoft computer). cpc is my 
> multimedia (emu1212m soundcard, printer is attached, DVD burner, 
> audacity) and production machine for my guitar lessons business. ppc is 
> the administrative computer (spreadsheets, documents, artwork) for the 
> business. dpc is my daughter's machine which has our first non-rpm-based 
> distro (ubuntu) - that's the machine I'll be setting up to use gtkpod 
> with the 3rd gen. iPod video nano. bpc is my son's computer - he doesn't 
> do much with it right now (just homework).
> 
> cpc: 20 GB master hard drive (that just died) and 10 GB slave hard drive 
> (I keep .ogg's on it), 384 MB RAM, PIII 733 MHz
> 
> ppc: 20 GB master hard drive and 6 GB slave hard drive (for backups), 
> 256 MB RAM, AMD Duron 800 MHz
> 
> dpc: 13.5 GB hard drive, 256 MB RAM, PIII 733 MHz
> 
> bpc: 13.5 GB hard drive, 256 MB RAM, PIII 733 MHz
> 
> My two goals are 1. backup, and 2. low down-time when a hard drive goes. 
> For instance, this hard drive crash I lost some data (not much because I 
> do backups, but some), and my production machine will be down for a 
> while because I have to install so much software (OS, apps, printer, 
> netwrok printing).
> 
> I just bought two identical 160 GB WD hard drives. So, I could set up 
> software RAID 1 as Lennart suggested - it would be the first time doing 
> this. How much slower will my computer really be due to the mirror? Will 
> I take a hit, say, when recording in audacity? Are RAID 1 cards cheap? 
> Would that give me hardware RAID and would the performace gain be worth 
> the effort? Are there any other solutions you guys suggest looking at 
> given the machines I have and all the hard drivves on them that coulkd 
> be redistributed? the only hard drive that is married to a machine is 
> the 20 GB hard drive on ppc (it's working real good for what my wife 
> needs so I don't want to mess with it - anything else is possible, though...

There will be no performance hit.  In fact there is a performance gain
since reads are distributed between the two disks as far as I understand
it.  So writes are same speed, and reads are faster.  And downtime is
reduced to near nothing since you only lost one of the disks in the
mirror and can quickly replace it and rebuild without any loss of data
and without having to reinstall everything.

Of course raid is NOT a backup and never will be.  It is protection
against disk failure only, although compared to backup this generally
saves you a ton of work in case of failure, while a backup protects you
against corruptions and mistakes by letting you recover lost files,
although generally it can be more time consuming to do so.

Where I work we actually backup a couple of servers using an external
500GB WD SATA driver in a NexStar3 eSATA/USB enclosure.  We rsync to it
every night, and have 3 disks on rotation being switched every friday.
We also mirror files between two servers, and keep rsnapshot archives of
the files on the server every 2 hours.  rsnapshot means you never loose
more than 2 hours worth of work if you accidentally delete or overwrite
or corrupt a file and it is trivial to access (we have it available as a
read only file share), the mirroring between servers (every 4 hours)
using rsync helps protect against loosing the filesystem, raid 1 takes
care of disk failures, and the backup gets the data off site once a week
just in case something very bad was to happen.  Using multiple disks
means there is always one disk off site, and when updating one disk
there is two others with previous versions that are not being touched
(one off site and one waiting to be swapped in).  Cost of each external
driver was about $100 for the disk and $45 for the enclosure. so less
than $600 for all 3.  We used to use DVDs but they are too slow, too
much hassle, and what do you do with the old versions after they start
to pile up.  Not very environmentaly friendly.  Destroying them with a
hammer was determined to be dangerous by the person who tried that
aproach.

--
Len Sorensen
--
The Toronto Linux Users Group.      Meetings: http://gtalug.org/
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://gtalug.org/wiki/Mailing_lists