Very Computer

Hello,

I am in the process of setting up a IDE RAID array on a soon-to-be Linux
machine.

I have a IDE controller combined with the mother board that can support up to 7
IDE devices.

I plan on using 5 various sized hard drive from different manufactures. (I
don't think there will be a problem with this)

My questions is:  How should I set the jumper settings?  All master or all
slaves?

Thanks in advance for your input.

Cheers,

Chad

Quote:> Hello,

> I am in the process of setting up a IDE RAID array on a soon-to-be Linux
> machine.

> I have a IDE controller combined with the mother board that can support up
to 7
> IDE devices.

> I plan on using 5 various sized hard drive from different manufactures. (I
> don't think there will be a problem with this)

> My questions is:  How should I set the jumper settings?  All master or all
> slaves?

Are your sure its IDE and not SCSI?

I thought IDE only allowed two devices per controller.

JP

On Thu, 19 Sep 2002 20:33:13 +0100, JP staggered into the Black Sun and
said:

Exactly the way the manual that came with the card tells you to set
them.  My guess would be to set all the drives to "master".

Quote:> Are your sure its IDE and not SCSI?  I thought IDE only allowed two
> devices per controller.

3Ware make a number of IDE hardware RAID cards.  These cards have a
dedicated processor and 3 to 7 IDE channels on them.  Each drive that
you connect has its own channel, minimizing bus contention (since IDE is
brain-damaged when it comes to bus sharing) leading to greater speed.
The entire array, once the appropriate kernel module is loaded, looks
like a big SCSI disk to the kernel.

t0rk may wish to reconsider his decision to use drives of differing
sizes.  If you have drives of 9, 12, 15, 18, and 21G, and you combine
them all in a RAID-5, you will end up with a usable capacity of
(totaldrives - 1)*(size of smallest drive) in the array.

--
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
Brainbench MVP for Linux Admin /
http://www.brainbench.com     /  "He is a rhythmic movement of the
-----------------------------/    penguins, is Tux." --MegaHAL

Quote:> t0rk may wish to reconsider his decision to use drives of differing
> sizes.  If you have drives of 9, 12, 15, 18, and 21G, and you combine
> them all in a RAID-5, you will end up with a usable capacity of
> (totaldrives - 1)*(size of smallest drive) in the array.

Thanks for the response.  I was under the assumption that I would be
able to use the total capacity of all the drives.  Thanks for pointing
this out.

Just to make sure I understand you clearly, if I use the same sized
drives you used in your example I would have the capacity of 36 gigs?

What I don't understand about the capacity formula is why do you have
to minus one drive? Does this mean if I have five (5) 10G hardives I
will have the capacity of 40G?

Thanks,

On 23 Sep 2002 11:36:11 -0700, t0rk staggered into the Black Sun and
said:

Quote:>> t0rk may wish to reconsider his decision to use drives of differing
>> sizes.  If you have drives of 9, 12, 15, 18, and 21G, and you combine
>> them all in a RAID-5, you will end up with a usable capacity of
>> (totaldrives - 1)*(size of smallest drive) in the array.

> I was under the assumption that I would be able to use the total
> capacity of all the drives.  What I don't understand about the
> capacity formula is why do you have to minus one drive?

'Cause that's the way RAID-5 works.

When you use RAID-5, each disk in the array is broken up into chunks
("stripes").  As an oversimplistic example, consider a 3-disk RAID-5,
each disk having 3 chunks.  The array will be laid out like so:

          chunk 0     chunk 1     chunk 2
disk 0    data0       data1       parity 3,5
disk 1    data2       parity 1,4  data3
disk 2    parity 0,2  data4       data5

The "parity" chunks are special.  Each bit in the parity chunk is 0 if
the corresponding bits in the other chunks in its column add up to an
odd number.  The parity bit is 1 if the corresponding bits add up to an
even number.

This parity information allows you to rebuild the array *without losing
data or having downtime* if a single disk fails.  That's the whole point
of RAID.  If you don't have parity bits, you have no Redundancy.  You
are trading away 1 disk's worth of space for the peace of mind that
comes from knowing you're protected against a single-disk failure.

NOTE:  Lose 2 disks from this array, and you're screwed.  Delete all
your important files, and you're screwed.  RAID does not eliminate the
need for backups.

Quote:> Does this mean if I have five (5) 10G hardives I will have the
> capacity of 40G?

Yep.  It might be worth your while to look at the RAID-HOWTO if you're
going to be using RAID in any production work.

--
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
Brainbench MVP for Linux Admin /
http://www.brainbench.com     /  "He is a rhythmic movement of the
-----------------------------/    penguins, is Tux." --MegaHAL