On Sep 25, 2010, at 9:11 AM, Christopher Chan christopher.chan@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