[SATLUG] Establishing a new network - Basic Question

[Travis]

> I would love to have the money
> and expertise to 
> establish a hot-swappable server set-up with DAT
> backup, but I really can't 
> afford a rack mountable server set-up with an
> expensive tape back-up system.

I don't think it needs to be rack-mount (overpriced). 
I was thinking of a regular commodity case.  The
drives could be something like SCA, or whatever is the
modern/cost-effective equivalent (SATA?).  Maybe you
can even do it with commodity drives (EIDE) and some
kind of backplane, I'm not really sure, which is why I
asked for info if you're researching it.

I got an 8-tape DAT changer for like $300.  A bit
pricey, I'll admit, but it's a one-time cost.  My
current filestore involves two WD 8MB 120GB EIDE
drives on two seperate hosts with nightly rsync
mirroring.  My Pentium-class servers were given to me
as junk, but I bet you could find some complete
systems that are perfectly up to the task for about $5
each.

> Either way, that still leaves teh question of "how"
> to set things up short 
> of hiring someone else to do it (another recurring
> expense).

Here's what I'm doing:
1) Buy a WD 120GB 8MB HDD off ebay for $80.
2) Plug it as the second drive into a computer already
running Linux ("main host").  Format it, mount it.
3) Repeat steps 1 and 2 for a "backup host".
4) Network the two hosts.
5) Write a cron job to rsync between the two file
systems every night.
6) Configure main host to export drives via NFS.
7) Network any client hosts with the servers.
8) Configure Linux client hosts to mount drives via
NFS from the main host.

Now you have your data resistant to drive failure
(main drive loss means up to 24 hours of transactions
lost, backup drive failure means no loss), and you
have resistance to accidental deletion (as long as you
catch it before the next rsync).

For a setup with HW RAID I imagine it's similar except
that the main host has some kind of hardware drive
array and involves more disks (min 3 for RAID 5, 2
otherwise).  There is software RAID if you don't need
hot-pluggability, but last time I worked with it the
fsck took a long time (I think it rebuilt the parity
info every time it booted).  Either way, it buys you
resistance to drive failures in the main host (which,
if you'll recall, could result in 24 hrs lost data).

Throw a tape drive in and you can recover from
accidental deletions much longer after the fact.  But
pulling from tape is a hassle so it's nice to have
that backup server with yesterday's data online in
secondary storage.  There's a good O'Reilly book on
Unix Backup and Recovery.

For redundancy against environmental disasters (house
fire, acts of godzilla), keep the backup server at a
friend's place (rsync over ssh).  Or set up a mutual
backup arrangement where you each back each other's
data up.

> If you are 
> really interested in exploring how to setup a setup
> such as you describe and 
> have deep pockets, I would be happy to point you to
> several consultants that 
> would be happy to take your money and set it up for
> you as well as set up a 
> mainenance program.

I have a brain and I'm not afraid to use it.
Why would I need a consultant?

> both things I can't afford
> right now and besides, I 
> want to understand how the whole thing works.

You have to pin down what you're trying to do before
you can learn how to do it.  I was trying to help you
in that regard with some suggestions.  You seem
dismissive and ungrateful.  If you want instructions
that a trilobyte can follow, you'll have to ask
someone else because this email has exhausted my
interest in helping you.


		
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