[linux-lvm] JBOD/NRAID configuration with LVM (repost)

[linux-lvm] JBOD/NRAID configuration with LVM (repost)

[Florian Lindner]

Since I've gotten no replies at all, I dare to repost...

Hello,
I'm the administrator of a file server from a student residential  
accommodation (from Munich, so pardon my English).

The machine is an ordinary PC (currently one HD for system, one for  
data, both paralell ATA). Due to the intendend use storage space is a  
primary issue while data safety is not too important neither is speed.  
Since money is also always low we need to be flexible with how we use  
the harddisks. For example it's unlikely to be possible to buy two or  
more identic harddisk to form a RAID 0.

My idea:

- Create an JBOD/NRAID of a all harddisks (except the system disk)

- The JBOD should be flexible when it comes to removing or adding  
another disk. For example if I want to remove a harddisk I a) unmount  
the JBOD b) say some kind of tool to free the harddisk to remove as  
completely as possible c) remove the disk software and hardware wise.

- If we manage to get our hands on another harddisk it is added to the  
volume. It there are already more than three disk present it replaces  
the smallest one.

- Hot swapping is not important. I don't think it's possible anyway  
due to the desktop PC hardware

- If a disk is broken the data loss should be limited to the data that  
actually is on that disk, the rest of the JBOD should remain  
functional (it is ok if it is not functional before a manual repair run)

How far is this possible with LVM? The distribution is Debian etch.

Thanks,

Florian

Re: [linux-lvm] JBOD/NRAID configuration with LVM (repost)

[Chris Cox]

On Wed, 2008-04-02 at 17:17 +0200, Florian Lindner wrote:
...snip...
> My idea:
> 
> - Create an JBOD/NRAID of a all harddisks (except the system disk)
> 
> - The JBOD should be flexible when it comes to removing or adding  
> another disk. For example if I want to remove a harddisk I a) unmount  
> the JBOD b) say some kind of tool to free the harddisk to remove as  
> completely as possible c) remove the disk software and hardware wise.
> 
> - If we manage to get our hands on another harddisk it is added to the  
> volume. It there are already more than three disk present it replaces  
> the smallest one.
> 
> - Hot swapping is not important. I don't think it's possible anyway  
> due to the desktop PC hardware
> 
> - If a disk is broken the data loss should be limited to the data that  
> actually is on that disk, the rest of the JBOD should remain  
> functional (it is ok if it is not functional before a manual repair run)
> 
> How far is this possible with LVM? The distribution is Debian etch.

IMHO, the safest way it to segment your data areas into multiple
filesystems rather than (you can use LVM areas, just not leverage
it for what you are asking for) using LVM.

Just my opinion.

By using separate filesystems (possibly separate VGs in your
situation), you can bring a new drive into a VG holding the
partitions you want to migrate to the larger drive (pvmove) and
the after that, remove the old smaller drive from that VG
and ultimately the system.

You might be able to create some kind of mess using contiguous
allocation of LVs ... but I personally would not recommend it
(makes way too many assumptions about things... loses flexibility).