Re: [PATCH] RAID10 and RAID6
martin f krafft <madduck@debian.org> writes:
> also sprach Ryan Niebur <ryanryan52@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.
>> + 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.
> 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.
MfG
Goswin
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