[CentOS] extend raid volume - new drive

Toby Bluhm tkb at alltechmedusa.com
Tue Apr 28 13:29:49 UTC 2009


dnk wrote:
> Hi there, I have a system with the following:
> 
> # fdisk -l
> 
> Disk /dev/sda: 80.0 GB, 80000000000 bytes
> 255 heads, 63 sectors/track, 9726 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
>     Device Boot      Start         End      Blocks   Id  System
> /dev/sda1   *           1          13      104391   83  Linux
> /dev/sda2              14        9471    75971385   83  Linux
> /dev/sda3            9472        9726     2048287+  82  Linux swap /  
> Solaris
> 
> Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
>     Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1   *           1      121601   976760001   fd  Linux raid  
> autodetect
> 
> 
> Disk /dev/sdd: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
>     Device Boot      Start         End      Blocks   Id  System
> /dev/sdd1   *           1      121601   976760001   fd  Linux raid  
> autodetect
> 
> Disk /dev/md0: 1000.2 GB, 1000202174464 bytes
> 2 heads, 4 sectors/track, 244189984 cylinders
> Units = cylinders of 8 * 512 = 4096 bytes
> 
> Disk /dev/md0 doesn't contain a valid partition table
> 
> 
> Now I just added a new hard drive (sdc).
> 
> I was wondering how to go about (if possible) to add this drive to my  
> existing partitions with LVM.
> 
> Now I never setup this system (Another person had), and if i am  
> reading the above right, it appears as though they did not use LVM for  
> the raid.
> 
> The system has the OS on a standalone drive, the home folder is on the  
> two raided drives. I was hoping to extend my home folder to take  
> advantage of my new drive.
> 
> Recommendations?

WHat size is the new disk? If it's 1GB, you have many options. If not, 
there will be trade offs getting it into your system.

If 1G, then

- add disk to md0 for 3 way mirror.
no increase in space, added safety/redundancy, current data kept.

- convert to raid5
increase in space, slight reduction in safety/redundancy, current data kept.

- convert all to LVM
flexible, largest storage, no redundancy, current data kept.

- convert to raid0
fast, largest storage, no redundancy, not flexible as LVM, destroys 
current data.


If the third disk in not 1GB, then

- convert to any raid
available space will be dictated by the smallest device/partition, 
wastes disk space, same other raid features as above.

- convert all to LVM
flexible, largest storage, no redundancy, current data kept.

- keep md0 as is, add sdc as a separate mount.
easy, not flexible storage, reduced safety/redundancy, current data kept.

- trade for a 1G disk.



-- 
tkb


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