[Gllug] Production system - Linux 2.4.24, LVM and cciss

[Dale Gallagher]

Hi Simon

You have made some very pertinent points!  I definitely need advice at
this stage, as the solution I'm building is quite ambitious and
reliability/backups are vital.  As soon as I have the budget, I'll
invest in an appropriate tape solution...

> You're considering RAID with high redundancy for your filesystem so I
> presumably don't need to tell you how likely and often disks fail -
> your proposed system is twice as likely to fail as a single disk, and

but more resilient overall really... if a disk (or two under
particular circumstances) fails, the array continues without data loss,
whereas the loss of a lone disk leads to data loss _and_ downtime.

> if it does you loose 50% of your backups instantly.

How so?

> I would suggest that the proposed system is only good for disaster
> recovery, because it gives little protection against user error
> destroying files (or contents) or software or hardware error
> corrupting files - you only have two backups, which isn't much history
> if you backup every day, as you should (and if you only backup once a
> week I hope you're sure that your users don't mind loosing up to a
> weeks worth of work/mail/whatever!).

For now, I'll run incremental daily data backups and bring one of the
disks off-site once a week and backup this backup to IDE-disk at the
office. As the user-base increases to a point where this is no longer
possible, realistically viable, or I have the budget, I'll upgrade to a
tape backup solution.  I'll be backing up system files to CD once a
week (the box will have a DVD/CD-RW drive), or after significant changes
to the system, whichever occurs first.

> So I would disagree with your assertion that tape is more susceptible
> to data corruption than disk for the above reasons - what is the your
> reasoning?

My (current) choice is based on budget, complexity and available time
for backup management... I _will_ address these issues sooner rather
than later and am now even more aware of the risks than before.

I think the ideal setup would really be:

4 disks in RAID1+0 config (slots 0-3)
1 hot spare in slot 4
1 Hotplug AIT drive in slot 5 (available in the HP-DL380)

With daily and weekly tape backups.  Any comments on this and my current
(interim) backup plan, now that you have more detail?

Thanks for your feedback!  I'd appreciate any further advice.

Regards
Dale
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