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tudor -Reinstate Monica-
Asked: 2018-09-17 06:23:12 +0800 CST

(Why) Does lvmraid6 need 5 drives?

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I'm investigating using LVMRAID instead of MD+LVM. In my case, I'm looking at a RAID6.

As expected, the docs say you need N+1 devices for RAID5, and a minimum of 3 drives.

The docs say for RAID 6 you need N+2.

However, it then says that the minimum drives required is 5.

In an MD RAID6, only 4 drives are required. So if I built RAID6+LVM I'd only need 4 drives whereas, according to the docs, I'd need 5 drives for LVMRAID6.

Does LVMRAID6 really need 5 drives?

If so, why does it need 5 drives rather than MDRAID6's 4 drives?

lvm

1 Answers

  1. Best Answer

    This seems to be hardcoded in the source code. Here a minimum of 3 stripes is the minimum, which excludes the parity disks. So that in turn is 5 disks for a RAID6.

    Unfortunately the commit message does not show the motivation behind the decision. You might want to ask this on the linux-vm mailing list.

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