Advice on build a RAID6

Advice on build a RAID6

[Krzysztof Adamski]

Hi All,

I have been tasked with creating a backup repository. I'm looking for
advice on building a (relatively) big RAID6 array. The array is to be
build with 12x 3T Hitachi drives. 
The plan is to have XFS on top of LVM on top of the RAID6 structure.
One requirement is to partition the drives at 99% for the RAID.
Majority of the RAID6 space will be used for the backups, ie files
larger then 4GB each in one LV, the rest will be minor and unimportant
for now. The read access will be sequential reading of the files via NFS
by a maximum of 5 processes.

Boot will be on a different array.

I know that to use larger then 2T partitions in the RAID I can't use
0.9, so which one to use?

This will be done on Debian Squeeze with standard packages.

Thanks in advance,
K

Re: Advice on build a RAID6

[Mikael Abrahamsson]

On Fri, 21 Oct 2011, Krzysztof Adamski wrote:

> One requirement is to partition the drives at 99% for the RAID.

Why? What problem are you solving by using partitions?

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se

Re: Advice on build a RAID6

[Krzysztof Adamski]

On Sat, 2011-10-22 at 10:54 +0200, Mikael Abrahamsson wrote:
> On Fri, 21 Oct 2011, Krzysztof Adamski wrote:
> 
> > One requirement is to partition the drives at 99% for the RAID.
> 
> Why? What problem are you solving by using partitions?
> 

There are at least two, you get to control the size of the area used
instead of depending the size of the drive, if in the future you change
a drive with a different make/model that is a bit smaller, you don't
have problems then.

You can store extra information in a second partition that may help you
with future recovery.

When you have lots of drives in a box (20 to 30) it makes it easy to
tell a new drive from an existing drive by looking at the partition
table. You can't count on device names in case of problems, since
usually you would have to reboot the box specially when it hangs.

This are just a few that I can think of from my experience managing
boxes with lots of drives and MD RAID for more then last 10 years.

I know that the only downside is that the partitions have to be
correctly aligned for the 4K drives, I don't know of any other reasons
not to use partitions.

K