RAID-5 (striping) without hardware support

[Tim Tipple_2]

I am setting up an HP-UX 10.20 system with five HotSwappable disks. Is it
possible to configure all five disks into a single RAID-5 disk array using
standard HP-UX software?

If not then the only alternative configuration I can see is to use mirroring
(RAID-1) to create two volume groups each containing two of the disks. The main
problem with this is that the remaining fifth disk cannot be mirrored and is in
effect "wasted".

Are there any other problems with this setup or is there a better way that
makes use of the fifth disk?

[Carlos Riera]

LVM software do by logical volume, not by Phisycal Volume, neither Volume
Group. It means you can make mirror for lvol1 and not for lvol2.

You can create 5 phisycal volumes, and create just 1 vg containing all 5 PV.

LVM ensure than 1 Logical extension(LE) ( 4 Mb) and its mirrored LE never will
be on same PV.

You must take special care with swap and dump lvs, because they need to
contigous, and no NO REALOCATION.

Finaly you can let LVM make things as it want, or you can specify where you
want your mirror copy.

This is true even you want to use striped facilities. HP call it EXTEND BASED
STRIP MIRROR ( or something like this).

[Melvyn Burnard_1]

To answer the first question, No you cannot set this up in a RAID 5
configuration, as this is done in hardware via the RAID controller.

As far as the Mirroring is concerned, you would have to have any disc with a
logical volume on it in the SAME volume Group as the mirroring disc.
You also do not mirror physical discs, but logical volumes, which can span
discs.
Therefore, if needed, you could set up logical volumes across 2 1/2 of the
physical discs, and then mirror these logical volumes in such a way that the
mirros are NOT on the same physical disc.


May I suggest you go to the attached URL and have a read through the manual
section Administering a System, which has most of what you would need to do
this.