How to create a terabyte storage array?

[Anders Karlsson]

On 12/1/05, 'Forum Post <ulist at gs1.ubuntuforums.org> wrote:
>
> How difficult is it to extend a Raid 5?

You don't.

>  Do you always need 5 drives?

You need at least 3 discs (2+P) and RAID-5 does not have a dedicated
parity disc, the parity data is evenly spread across all discs in the
array.

>  I currently have a RH8 server with mirrored 80GB drives that I'm now out
> of room on.  I want to upgrade it to Ubuntu and I don't want to dump a
> ton of money into 4 or 5 drives.  Since the data on it doesn't change
> very often (MP3's and family pictures), I have just bought a 250GB
> drive and planned on creating one LVM group with it and a 2nd LVM group
> with the two 80's.  I was then thinking of having a cron job run every
> night that backed up from one LVM group to the other, only copying
> files that have changed, been added, or removing ones that no longer
> exist.  If I need to extend either LVM group later, it's a non-issue.
> If one of the groups fail, it can be rebuilt from the other.

Sensible approach, you can use 'rsync' for the copy. It can be set up
to do exactly what you are describing.

> I know that RAID-5 gives you "instant" redundancy but I don't really
> need that with my setup.

Most people don't. I will explain why I suggested RAID-5 to the
original poster. The sheer size of the storage required. He needed 1TB
of storage space to serve up. Even with an AIT tapedrive that does
200/400GB per tape, he will have to swap tapes several times. The time
it takes to restore from tape compared to just having to replace a
drive makes it a fairly simple choice.

For a home user, it may be alright to spend a day re-creating the 1TB
filesystem because a disc died, and then spend a day or two restoring
from 3-4 tapes. But sometimes it is worth taking a leaf from the more
advanced SysAdmin's book and go that little further. If using RAID and
a disc dies, there is no downtime while sourcing a replacement (if you
REALLY value your data, then you have hot spares set up) and you can
carry on using the file server and carry on backing it up.

I have been in the position of NOT using RAID on a server, and not
having a proper backup scheme in place. I am sticking that tapedrive
back in as soon as I can... And I am now using RAID-1 and '-o sync' on
the filesystems I really value.

--
Anders Karlsson <trudheim at gmail.com>