raid 0 on different size devices?

raid 0 on different size devices?

[Dan Egli]

Can the linux Software Raid handle devices of differing size? Basically my 
issue is this: I've got two drives, a 27GB and a 40GB. I really want to 
get them accessed as a single device. Is it possible to stack these drives 
using like a raid 0?

Thanks!
--- Dan

Re: raid 0 on different size devices?

[seth vidal]

On Wed, 2003-11-19 at 13:57, Dan Egli wrote:
> Can the linux Software Raid handle devices of differing size? Basically my 
> issue is this: I've got two drives, a 27GB and a 40GB. I really want to 
> get them accessed as a single device. Is it possible to stack these drives 
> using like a raid 0?

yes - but having the both be the same speed would be a good thing.

-sv

Re: raid 0 on different size devices?

[Hermann Himmelbauer]

On Wednesday 19 November 2003 20:00, seth vidal wrote:
> On Wed, 2003-11-19 at 13:57, Dan Egli wrote:
> > Can the linux Software Raid handle devices of differing size? Basically
> > my issue is this: I've got two drives, a 27GB and a 40GB. I really want
> > to get them accessed as a single device. Is it possible to stack these
> > drives using like a raid 0?
>
> yes - but having the both be the same speed would be a good thing.

AFAIK they have to be of equal size but as you can create a 27GB partition on 
the 40GB drive, you could at least get 54GB out of this configuration. 

I have never used it but I think that LVM can also do just that: Concatenate 
multiple physical disks to one big logical.

If one disk is a lot slower than the other it could happen that the RAID0 is 
slower than the single disk.

		Best Regards,
		Hermann

-- 
x1@aon.at
GPG key ID: 299893C7 (on keyservers)
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Re: raid 0 on different size devices?

[seth vidal]

> AFAIK they have to be of equal size but as you can create a 27GB partition on 
> the 40GB drive, you could at least get 54GB out of this configuration. 

No. I have a 120GB and a 60GB disk in a linear array working just fine.

it's not technically raid0, but it lets the person do what they're
wanting to do.

-sv

Re: raid 0 on different size devices?

[Dan Egli]

On 19 Nov 2003, seth vidal wrote:

> 
> > AFAIK they have to be of equal size but as you can create a 27GB partition on 
> > the 40GB drive, you could at least get 54GB out of this configuration. 
> 
> No. I have a 120GB and a 60GB disk in a linear array working just fine.
> 
> it's not technically raid0, but it lets the person do what they're
> wanting to do.

How do I setup a linear array?

--- dan

Re: raid 0 on different size devices?

[seth vidal]

> How do I setup a linear array?

a raidtab for use with mkraid might look something like this:
raiddev             /dev/md0
raid-level                  linear
nr-raid-disks               2
chunk-size                  32
persistent-superblock       1
    device          /dev/hda1
    raid-disk     0
    device          /dev/hdc1
    raid-disk     1


or you can use mdadm -C -llinear etc etc etc - man mdadm for complete
options.

-sv

Re: raid 0 on different size devices?

[Jose Luis Domingo Lopez]

On Wednesday, 19 November 2003, at 13:01:10 -0700,
Dan Egli wrote:

> How do I setup a linear array?
> 
Maybe you should give LVM a try if you just want to set up a linear
array, to aggregate disk space into one (large) block device. With LVM
you have all the features of a linear RAID array and more, for example
it is possible to add more drives at a later time and give the added
space to the LV (equivalent to a partition).

Better than trying to explain in two lines what LVM is, have a look at
LVM-HOWTO at http://tldp.org/HOWTO/LVM-HOWTO/

Greetings.

-- 
Jose Luis Domingo Lopez
Linux Registered User #189436     Debian Linux Sid (Linux 2.6.0-test9-mm3)

Re: raid 0 on different size devices?

[Neil Brown]

On  November 19, skvidal@phy.duke.edu wrote:
> 
> > AFAIK they have to be of equal size but as you can create a 27GB partition on 
> > the 40GB drive, you could at least get 54GB out of this configuration. 
> 
> No. I have a 120GB and a 60GB disk in a linear array working just fine.
> 
> it's not technically raid0, but it lets the person do what they're
> wanting to do.
> 

The 'md' driver will let you set up an 'raid0' array using these two
drives.  This will result in a 180GB array.

The first 120 Gb will be striped over the two drives.  The remaining
60Gb will simply be the end of the larger drive.

You can, ofcourse, also set up a linear array.

man md

(with mdadm installed).

NeilBrown

Re: raid 0 on different size devices?

[Mike Dresser]

On Wed, 19 Nov 2003, Dan Egli wrote:

> Can the linux Software Raid handle devices of differing size? Basically my
> issue is this: I've got two drives, a 27GB and a 40GB. I really want to
> get them accessed as a single device. Is it possible to stack these drives
> using like a raid 0?

Yes.  Years and years ago I did this with 10 drives (6 scsi, and 4 ide).

Remember that a drive failure on any disk is going to trash the entire
array.

There's also a linear raid mode that works the same basic idea as raid0,
in Linux.

Mike