[CentOS] RAID, LVM, extra disks...

[Alain Spineux]

On Nov 29, 2007 6:59 AM, Ugo Bellavance <ugob at lubik.ca> wrote:
> Hi,
>
>         This is my current config:
>
> /dev/md0 -> 200 MB -> sda1 + sdd1 -> /boot
> /dev/md1 ->  36 GB -> sda2 + sdd2 -> form VolGroup00 with md2
> /dev/md2 ->  18 GB -> sdb1 + sde1 -> form VolGroup00 with md1
>
> sda,sdd -> 36 GB 10k SCSI HDDs
> sdb,sde -> 18 GB 10k SCSI HDDs
>
> I have added 2 36 GB 10K SCSI drives in it, they are detected as sdc and
> sdf.
>
> What should I do if I want to optimize disk space?
>
> The simplest solution would be to create /dev/md3 out of sdc1 and sdf1,
> and add it to the VG, and increase the size of my /vz logical volume.
>
> However, if I could convert that to a RAID5 (it could be possible to
> re-install, but I would rather not), I could have 6 drives in RAID5, so
> I'd have 5x36 GB (180) of space available total, instead of 3*36 (108).

180, you mean 2 X 5x18

Yes and without rebooting :-)

- break the 36GB mirror (using mdadm, faile /dev/sdd2, and then remove it),
- break the 18GB mirror (using mdadm, faile /dev/sde1, and then remove it),
- create sd[cf][123] of 200Mb, 18G, 18G (the 200Mb is useless but to
keep the same partitioning schema)
- create a _degraded_ raid5 with sd[cfd]2 sde1 named /dev/mdX
- vgextend your VolGroup00 to use this new partition.
# pvcreate /dev/mdX
# vgextend VolGroup00 /dev/mdX
- then move all PE  on md1  to mdX
# pvmove /dev/md1/dev/mdX
- then remove md1 from the VG
# vgreduce VolGroup00  /dev/md1
- now you dont need md1 anymore, stop it (sorry I'm less  skilled with
mdadm command, without manual page )
- now add /dev/sda2 to your _degraded_ raid 5

et voila for the first raid5

do the same with the second one


Regards

>
> Also, please note that this is a Dual PIII 1.2 Tualatin. I'm runing
> OpenVZ with virtual machines that are not really CPU expensive, but I
> would not like to see my processors spending most of their time
> computing XORs for the RAID5.
>
> Any suggestions/tips welcome.
>
> Regards,
>
> Ugo
>
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-- 
Alain Spineux
aspineux gmail com
May the sources be with you