Configuring RAID5 w/ Spare?

Configuring RAID5 w/ Spare?

[Carlos Mennens]

 have a machine that supports 4 S-ATA drives. I have all identical
drives in each slot. I am asking for someone to please tell me how I
can create a RAID5 array on Linux and then also have the 4th drive
(/dev/sdd) as a hot spare for any of the three drives in the array /
volume?

I did the following:

/device = type @ parition size

/dev/sda1 = fd @ 100 MB (bootable for /boot)
/dev/sda2 = fd @ 1 GB (Going to be used for Swap)
/dev/sda3 = fd @ 300 GB (Going to be used for /)

Now I make the same thing for /dev/sdb & /dev/sdc. I DON'T PARTITION
OR FORMAT /dev/sdd.

Now I am creating my RAID and this is where I am confused. How do I
correctly issue the 'mdadm' command to create the volumes for my
filesystem and also utilize /dev/sdd as a hot spare?

(/boot)

mdadm --create /dev/md0 --level=1 --raid-devices=3 /dev/sda1 /dev/sdb1
/dev/sdc1 --spare-devices=1 /dev/sdd
(Swap)

mdadm --create /dev/md1 --level=1 --raid-devices=3 /dev/sda2 /dev/sdb2
/dev/sdc2 --spare-devices=1 /dev/sdd
(/)

mdadm --create /dev/md2 --level=5 --raid-devices=3 /dev/sda3 /dev/sdb3
/dev/sdc3 --spare-devices=1 /dev/sdd
Is that correct above or would I 1st have to partition the /dev/sdd drive?

Re: Configuring RAID5 w/ Spare?

[Brendan Conoboy]

On 03/11/2010 11:11 AM, Carlos Mennens wrote:
> Now I make the same thing for /dev/sdb&  /dev/sdc. I DON'T PARTITION
> OR FORMAT /dev/sdd.

Why not partition?  It's possible to create a floating spare, but it 
doesn't really make sense for the configuration you've described.  Just 
add identical partitions on sdd and include the respective partitions on 
each of your array creation commands.

-- 
Brendan Conoboy / Red Hat, Inc. / blc@redhat.com

Re: Configuring RAID5 w/ Spare?

[Carlos Mennens]

On Thu, Mar 11, 2010 at 1:16 PM, Brendan Conoboy <blc@redhat.com> wrote:
> Why not partition?  It's possible to create a floating spare, but it doesn't
> really make sense for the configuration you've described.  Just add
> identical partitions on sdd and include the respective partitions on each of
> your array creation commands.

OK so you're just saying all I should change is partition /dev/sdd as
I did the rest? I don't however need to format this when installing my
Linux O.S., correct? I should just skip formatting and mount point
assignment since it's a hot spare?
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Re: Configuring RAID5 w/ Spare?

[Brendan Conoboy]

On 03/11/2010 11:18 AM, Carlos Mennens wrote:
> OK so you're just saying all I should change is partition /dev/sdd as
> I did the rest? I don't however need to format this when installing my
> Linux O.S., correct? I should just skip formatting and mount point
> assignment since it's a hot spare?

Right.  In reality the only "formatting" that takes place on these 
partitions is when you run the mdadm command: It combines the partitions 
according to your command line arguments, producing a new block device, 
/dev/mdX.  It's /dev/mdX that you format (or put LVM on, then create a 
physical volume.. then a volume group... then a logical volume... then 
format that with a filesystem).

-- 
Brendan Conoboy / Red Hat, Inc. / blc@redhat.com