some question in SoftRaid

some question in SoftRaid

[lilha]

hello,everyone.i am a freshman in linux raid.

i want to know some limits about raid,i try to find it in Raid-Howto and
Raid-FAQ,etc..
but i cann't find it.

Follow is my question:

1.Raid 0,1,5 must install in differ disk?right?
RAID-0 and RAID-1 need at lest 2 disk
RAID-5 need at lest 3 disk,is it right?
then is there any requrement about the partition Type(such as
primary,logical or extend partition )?

2.can i setup raid0,1,5 in the partition which has different size?
such as:
/dev/hda1 500M
/dev/hdc1 600M
can i setup raid-0 or raid-1?i try it,but failed.

3.how can I remove raid from disk?
such as,i have md0(RAID 0),it use /dev/hda2 and /dev/hdc2
now i want to these partitions don't use raid,i want to release these
partition
then how can I do?


thanks a lot.

Regards, echo

Re: some question in SoftRaid

[Danilo Godec]

On Thu, 23 May 2002 lilha@legend.com.cn wrote:

> 1.Raid 0,1,5 must install in differ disk?right?

Not really, you can make Linux SW RAID on any kind of partition - even on
the same disk. It really makes no sense, thouhg.

> RAID-0 and RAID-1 need at lest 2 disk
> RAID-5 need at lest 3 disk,is it right?

Right.

> then is there any requrement about the partition Type(such as
> primary,logical or extend partition )?

I think not. I'm not sure about the extended partitions, but primary and
logical should work.

> 2.can i setup raid0,1,5 in the partition which has different size?
> such as:
> /dev/hda1 500M
> /dev/hdc1 600M
> can i setup raid-0 or raid-1?i try it,but failed.

For RAID0, partitions should be approx. the same size, but it should work
in any case, however the striping will only be performed for the size of
the smaller partition. Maybe there is a treshold when the difference gets
to big...

You should also be able to create a RAID1 array with two different
partition sizes, however the resultin array will be the size of the
smaller partition. I'm not certain, but maybe the order is important - if
the smaller partition is listed first, the bigger will be partially used.
If the bigger is listed first, the smaller will end up being 'too
small'...

I'm not sure about RAID5, but I think the partitions should be the same
size (at least very close). At least that's how I do it.

> 3.how can I remove raid from disk? such as,i have md0(RAID 0),it use
> /dev/hda2 and /dev/hdc2 now i want to these partitions don't use
> raid,i want to release these partition then how can I do?

You can use 'the old' raidsetfaulty - raidhotremove combination, or you
can use the new mdadm. Both do the job.

If you use autodetection, you can also change the partition type from
'0xfd' to something else.

  D.

Re: some question in SoftRaid

[lilha]

Thanks a lot.
i have setup raid0 and raid1 in the same disk and
i also create a RAID1 array with two different partition sizes, the
resultin array is the size of the
smaller partition.(it don't care the order. )

but how to use raidhotremove combination or the new mdadm?
i try it:
#raidstop /dev/md3
#raidhotremove /dev/md3
No target disk specified!

is there any doc about how to remove raid?
and what is the new mdadm?

thank very much!

Regards, Echo

Re: some question in SoftRaid

[Danilo Godec]

On Fri, 24 May 2002 lilha@legend.com.cn wrote:

> but how to use raidhotremove combination or the new mdadm?
> i try it:
> #raidstop /dev/md3
> #raidhotremove /dev/md3
> No target disk specified!

If you want the array completely removed, you don't need to use the
'raidhotremove' command. This is intended for removing a block device from
the array.

And you don't have to stop the array. You can remove the disk from an
active array. For example, assuming that it is /dev/hda3 you want to
remove:

# raidsetfaulty /dev/md3 /dev/hda3
# raidhotremove /deV/md3 /dev/hda3

For completely removing the array you should just stop it (raidstop
/dev/md3) and change the partition types from 0xfd, so the kernel won't
autodetect them at next boot. Otherwise, after issuing the raidstop, the
array is stopped and the partitions should be usable.

> is there any doc about how to remove raid?

I think the RAID-HOWTO pretty much covers it.

http://unthought.net/Software-RAID.HOWTO/

> and what is the new mdadm?

mdadm is a new utility for managing Linux SW RAID. You should check the
archive of this list for more about it.

   D.