[PATCH] RAID10 and RAID6

[Ryan Niebur]

On Fri, Jul 18, 2008 at 01:28:26PM +0200, Goswin von Brederlow wrote:
> martin f krafft <madduck at debian.org> writes:
> 
> > also sprach Ryan Niebur <ryanryan52 at gmail.com> [2008.07.17.2137 +0200]:
> >> Here is a patch that adds support for RAID6 and RAID10 to the
> >> debian installer.
> >
> > Wow! Thanks!
> >
> >> +_Description: Number of active devices for the RAID6 array:
> >> + The RAID6 array will consist of both active and spare partitions. The active
> >> + partitions are those used, while the spare devices will only be used if one or
> >> + more of the active devices fail. A minimum of three active devices is
> >> + required.
> >
> > I think it's four, isn't it?
> 
> 3 is theoretical possible although it makes no sense. A raid1 with 2
> mirrors would be better there.
> 

Since the existing code for RAID5 requires 3 drives, I'm going to have the RAID6 code require 4 drives.

> >> + NOTE: this setting cannot be changed later.
> >
> > It can, but not trivially.
> >
> >> +Template: mdcfg/raid10devcount
> >> +Type: string
> >> +# :sl3:
> >> +_Description: Number of active devices for the RAID10 array:
> >> + The RAID10 array will consist of both active and spare partitions. The active
> >> + partitions are those used, while the spare devices will only be used if one or
> >> + more of the active devices fail. A minimum of four active devices is
> >> + required.
> >
> > You can have RAID10 across two devices, although it makes no sense,
> > really.
> 
> Raid10 allows different layouts. For a single stream access a 2 disk
> raid 10 with far copies reads twice as fast as raid1. Raid 1 only uses
> both disks when you have 2 streams reading.
> 
> Further raid10 over 3 devices with 2 copies makes sense too. It gives
> you 1.5* the space and can handle one disk failing without the cpu
> cost of raid5.
> 

In my next patch it is changed to a minimum of 2 for RAID10.

> > I haven't had time to look at your patch in depth, but it's looking
> > good. Unfortunately it's probably too late for lenny...
> 
> I haven't looked at the path either but I hope the raid10 asks for the
> number of copies and layout to be used. Those are important factors.
> If not then that would be an important feature that is missing.
> 

Yes, it does.

> MfG
>         Goswin

-- 
_________________________
Ryan Niebur
RyanRyan52 at gmail.com
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