Hardware RAID 5 - Need vinum?

Tony Shadwick tshadwick at goinet.com
Wed May 11 07:03:45 PDT 2005


The problem I've had in the past in Windows for example:

Drive D: is a RAID5 volume, 400GB, nearly full.  If I add a 200GB drive to 
the array, the 'disk' that Drive D: resides on is now ~600GB, but Drive D: 
will remain 400GB.  I would have to utilize a third party piece of 
software to resize Drive D: to utilize all 400GB, or create another 
partition to use that extra 200GB.

In my case. /media/video will still only have 400GB available to it.  I'm 
creating one partition on the array with one slice.  My understanding then 
is if I go into the label editor after adding my new drive, I'll have 
200GB of free space, and I could create another slice and another 
mountpoint, but not simply add that additional space to my original slice 
and mountpoint at /media/video.

Now, since I originally posted this message, I did more digging, and found 
some posts regarding growfs.  Perhaps that command is what I'm looking 
for, and would allow me to grow /media/video to use all 600GB in that 
case.

Now my only concern is whether or not the SX6000 support nondestructively 
growing a RAID5 array.  If I'm right about growfs that is. :)

On Wed, 11 May 2005, Subhro wrote:

> On 5/11/2005 2:35, Tony Shadwick wrote:
>
>> What my concern is when I start to fill up the ~400GB of space I'm giving 
>> myself with this set.  I would like to simply insert another 200GB drive 
>> and expand the array, allowing the hardware raid to do the work.
>
> That is what everybody does. It is very much normal.
>
>> 
>> The problem I see with this is that yes, the /dev/(raid driver name)0 will 
>> now be that much larger, however the original partition size and the 
>> subsequent slices will still be the original size. 
>
> I could not understand what you meant by RAID device entry would be larger. 
> The various entries inside the /dev are nothing but sort of handles to the 
> various devices present in the system. If you want to manipulate or utilize 
> some device for a particular device present on your box from a particular 
> application, then you can reference the same using the handles in the /dev. 
> And the handles remains the same in size irrespective of whether you have 1 
> hard disk or 100 hard disks in some kind of RAID.
>
>> Do I need to (and is there a way?) to utilize vinum and still allow the 
>> hardware raid controller to do the raid5 gruntwork and still have the 
>> ability to arbitrarily grow the volume as needed?  The only other solution 
>> I see is to use vinum to software-raid the set of drives, leaving it as a 
>> glorified ATA controller card, and the cpu/ram of the card unitilized and 
>> burden the system CPU and RAM with the task.
>
> The main idea in favor of using Hardware RAID solutions over software RAID 
> solutions is you can let the CPU do things which are more worthwhile than 
> managing I/O. The I/O can be well handled and is indeed better handled by the 
> chip on the RAID controller card than the CPU. If you add another disk to 
> your RAID or replace a dead disk at any point of time, then the RAID card 
> should automatically detect the change and rebuild the volumes as and when 
> required. This would be completely transparent to the OS and sometimes also 
> transparent to the user.
>
> Regards
> S.
>


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