[CentOS] Raid 10 questions...2 drive

Tom H tomh0665 at gmail.com
Sat Sep 25 13:52:35 EDT 2010

On Sat, Sep 25, 2010 at 11:48 AM, Ross Walker <rswwalker at gmail.com> wrote:
> On Sep 25, 2010, at 9:11 AM, Christopher Chan <christopher.chan at bradbury.edu.hk> wrote:
>> Jacob Bresciani wrote:
>>> RAID10 requires at least 4 drives does it not?
>>> Since it's a strip set of mirrored disks, the smallest configuration I
>>> can see is 4 disks, 2 mirrored pairs stripped.
>> He might be referring to what he can get from the mdraid10 (i know, Neil
>> Brown could have chosen a better name) which is not quite the same as
>> nested 1+0. Doing it the nested way, you need at least 4 drives. Using
>> mdraid10 is another story. Thanks Neil for muddying the waters!

> True, but if you figure it out mdraid10 with 2 drives = raid1, you would need 3
> drives to get the distributed copy feature of Neil's mdraid10.

I had posted earlier (
http://lists.centos.org/pipermail/centos/2010-September/099473.html )
that mdraid10 with two drives is basically raid1 but that it has some
mirroring options. In the "far layout" mirroring option (where,
according to WP, "all the drives are divided into f sections and all
the chunks are repeated in each section but offset by one device")
reads are faster than mdraid1 or vanilla mdraid10 on two drives.

> For true RAID10 support in Linux you create multiple mdraid1 physical
> volumes, create a LVM volume group out of them and create logical
> volumes that interleave between these physical volumes.

Vanilla mdraid10 with four drives is "true raid10".

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