Re: RAID questions

["A.Sajjad Zaidi" <sajjad@example.com>]

Jean-Christian Imbeault wrote:

> Ok, I've been doing some reading on RAID. I think I have the basics down but
> a few questions came up. Could some one clarify the following for me?
>
> 1- What's the advantage of RAID level 1 versus level 5? They both seem to
> offer redundancy.

RAID level 1(mirroring) only offers redundancy. That is, with 2 drives using
RAID level 1, you only get the capacity of one drive.

RAID 5 offers this as well as striping (concatinating 2 or more drives to form
1 large drive). So with 3 drives, you can have the space of 2 as well as
redundancy.

With both, you can set the system up so if one disk fails, another can take
over.

> 2- Is it still the case that you have the whole system under RAID. This
> because having system files and a bootable RAID system is contra-indicated.
> (Or at least causes so much sysadmin pain it's not worth it)

Not sure what you mean, but there is no problem with having the whole system on
RAID. Your boot loader and kernel should support booting off of RAID though.

> 3- How do you know when a disk has failed?

I run a script every minute to check /proc/mdstat for any error messages.

> 4- How easy is it to replace a failed disk and have the system back up?

If the system support hot-swapping, all you need to do is pull out the bad
drive and replace it with a good one. Assuming your system is configured
correctly, you wont have any downtime.

If it doesnt support hot-swapping, youll need to power off and do the
replacement.

> I'm thinking of setting up a mail server at out office and I was thinking
> that since it is somewhat of a mission critical system installing RAID would
> be a good idea. To protect against disk failure I tought RAID would be a
> good idea. But maybe there are better ways than RAID?

The more redundancy the better. You can have RAID and do regular offsite
backups.

Regards,

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