[CentOS] Re: Raid5 issues

[Ruslan Sivak]

Toby Bluhm wrote:
>> With raid 10, if it happens on one of the disks in the other set, you 
>> don't have a problem, and if it happens to the disk in the same set 
>> (not very likely),
>
> A 1 in 3 chance of putting the two worst disks together when using 4 
> disk raid10.
Yes, as in a 33% chance vs a 100% chance with raid5. 
>> I know there is a raid10 personality for md.  I saw it in the source 
>> code.  I see people's boot logs all over the web that say this:
>>
>> md: linear personality registered as nr 1
>> md: raid0 personality registered as nr 2
>> md: raid1 personality registered as nr 3
>> md: raid10 personality registered as nr 9
>> md: raid5 personality registered as nr 4
>>
>> Why does CentOS5 not support the raid10 personality?  Do i need to 
>> custom compile md?  Do I need to custom compile the kernel?  Russ
>>
>>
>
> You have enlightened me to the raid10 module:
>
> [root at tikal ~]#  locate raid10
> /usr/src/kernels/2.6.9-42.0.3.EL-smp-i686/include/config/md/raid10
> /usr/src/kernels/2.6.9-42.0.3.EL-smp-i686/include/config/md/raid10/module.h 
>
> /usr/src/kernels/2.6.9-42.0.3.EL-smp-i686/include/linux/raid/raid10.h
> /usr/src/kernels/2.6.9-42.0.10.EL-i686/include/config/md/raid10
> /usr/src/kernels/2.6.9-42.0.10.EL-i686/include/config/md/raid10/module.h
> /usr/src/kernels/2.6.9-42.0.10.EL-i686/include/linux/raid/raid10.h
> /usr/src/kernels/2.6.9-42.0.3.EL-i686/include/config/md/raid10
> /usr/src/kernels/2.6.9-42.0.3.EL-i686/include/config/md/raid10/module.h
> /usr/src/kernels/2.6.9-42.0.3.EL-i686/include/linux/raid/raid10.h
> /lib/modules/2.6.9-42.0.3.EL/kernel/drivers/md/raid10.ko
> /lib/modules/2.6.9-42.0.10.EL/kernel/drivers/md/raid10.ko
> /lib/modules/2.6.9-42.0.3.ELsmp/kernel/drivers/md/raid10.ko
>
> [root at tikal ~]#  modprobe raid10
>
> [root at tikal ~]#  lsmod | grep raid
> raid10                 23233  0
> raid1                  20033  1
>
> This is not a Centos 5 machine though, it's SL4.4.
>

Yes, this is exactly what I'm looking to use.  How would I go about 
enabling it on CentOS?

Russ