[CentOS] Raid 10 questions...2 drive

[Ross Walker]

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.

Mdraid10 actually allows for a 3 drive raid10 set. It isn't raid10 per say but a raid level based on distributing copies of chunks around the spindles for redundancy.

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.

This can give you the ability to extend a LVM RAID10 VG by adding RAID10 PVs to the VG. Unfortunately there isn't a resilver feature to LVM so you need to create a new LV to stripe it across all the members afterward, so leave room in the VG to do that.

-Ross