[Novalug] RAID use with two 1TB drives

[jecottrell3 at comcast.net]

Yes and no. RAID5 with two disks *is* RAID1, if you think about it.

It is tempting to think of RAID1 is "mirroring", but you can also think of the second disk as "even parity" or "the XOR of all the other disks".

And since both disks contain the same thing, it's easy enough to consider that the "parity" is "striped across 'all' disks".

Or in other words, RAID1 is a Degenerate Case of RAID5. Just like Disk Concatenation is a degenerate case of Disk Striping (with a "stripe width" equal to the "drive size").

But I notice that you said "best". Well, if you are going to be writing much, RAID5 pretty much sucks...pay the extra money and use mirroring.

Likewise, RAID6 is a Waste...better to use RAID5 with an array one disk wider...IFF you have Hot Swap. Without it...OK.

Also, realize that you can get a "RAID10" effect by mirroring sda1 with sdb2 and striping that against mirror(sdb1,sda2), but that only helps if specific surfaces go bad...not if the whole drive does.
 
AND...if you were to actually DO that, start your first partition at Cylinder 2 to avoid having the MBR steal space from you.

JIM

----- Original Message -----
From: "Jay Hart" <jhart at kevla.org>
To: novalug at calypso.tux.org
Sent: Sunday, February 12, 2012 9:41:31 AM
Subject: [Novalug] RAID use with two 1TB drives

Using FreeNAS, building new backup server.

I'm going to assume with 2 identical drives the best I can do is RAID1.  Looks
like RAID5 needs minimum 3 drives.

Am I correct is this assumption?  Would would be the best use of 2 drives and
FreeNAS?

Finally updating my old FreeNAS box, which is not using RAID.

TIA,

Jay

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