Re: Change from mirror to RAID

[Douglas Handy <dhandy1@xxxxxxxxxxxxx>]

Carl,

>I have a model 400 that ...  I will be adding a 7117 expansion cabinet to ...

>I would like to RAID all 8 drives in the same RAID set.  Can I do it ...?

The model 400, like my 40S with a 7117, does not support RAID on the MFIOP.
Only the drives in the 7117 expansion may be in the RAID set.   You may want to
consider moving the 2nd paid or 6607's from the MFIOP to the 7117 expansion
since it will hold up to 8 drives.

Leave one pair in the MFIOP to mirror the load source (yielding 4GB protected),
and six drives in the 7117 in a single RAID set (yielding 20GB protected) for a
total capacity of around 24GB.

If you leave the second mirrored pair on the MFIOP, you end up with about 20GB
total protected space (4 + 4 + 12).

As far as I can tell from playing with various drive configurations on my 40S,
where I currently have twelve 6606 drives, the 6502 will support anywhere from 4
to 8 drives in a RAID set.  But the actual RAID stripping seems to be across
exactly 4 or 8 drives.  If you establish a RAID set of 6 drives, it will make
four of them 75% capacity and the other two 100% capacity when you look at the
actual distribution.

I don't think this has much practical effect on distribution of disk arm
utilization, but it does mean you have a pretty simple way of migrating two
drives from the MFIOP to the 6502 RAID set.  Since the RAID stripping will be
across just four drives whether or not you initially put six drives in the 7117,
just install the 7117 and the four new drives first.  Configure the RAID set,
raising your system to 20GB effective capacity.

Now remove the 3rd & 4th drives on the MFIOP from the configuration.  The system
will migrate the data to the remaining disks (ie, the four new ones since they
have less usage than the first mirrored pair).  Once the data is transferred,
remove the drives, install in the 7117, and add to the RAID set.  This will
raise your effective capacity to 24GB.

Then balance the drive usage with STRASPBAL.

Doug