RE: Exposure with unprotected disk units -- MIDRANGE-L

You probably "could" add the 17.5 G drives to the parity set with the 4 G
units, but I don't think that you'd want to.  We had a single 2 G drive in a
parity set with 8 G drives once and the 2 G drive got overworked and killed
the I/O in that set.  I was told that the rule of thumb was not to mix
drives more than 1 step apart in a parity set.  Of course the rules could be
different now but I would think that they would be more dependant on the
disk controller than the drives themselves.

If you had a parity set with 8.5 G drives in it I wouldn't hesitate to add
the 17.5's to it.  Other options would be to buy two more 17.5's to add to
this set and start parity protection (you'll lose 25% of the total DASD) or
just start mirroring and lose 50% (you'd be at 37.2% in this ASP.)

Regards,
Scott Ingvaldson
AS/400 System Administrator
GuideOne Insurance Group

-----Original Message-----
date: Mon, 27 Oct 2003 13:47:41 -0600
from: "Scott Lindstrom" <SLindstrom@xxxxxxxxxx>
subject: Exposure with unprotected disk units


In reviewing one of the old systems I am responsible for, I noticed that
some 17.54gb disk units were added onto the system (as ASP 3) and are in an
unprotected state.  I think if we had added 4gb disk units in these
locations, we simply could have added them to the existing parity set, but
since they are 17.54gb they can't be added.  Is this correct?

                                  Size     %    I/O   Request   Read  Write
Read  Write     %       --Protection--
Unit  Type    (M)  Used    Rqs  Size (K)    Rqs    Rqs    (K)    (K)  Busy
ASP  Type  Status
   1  6607   4194  84.8     .5      10.3     .3     .2   12.5    6.7     0
1  DPY   ACTIVE
   2  6607   3670  84.7     .5      15.3     .3     .2   18.6   11.4     0
1  DPY   ACTIVE
   3  6607   3670  84.7     .5      18.2     .2     .2   24.0   10.9     0
1  DPY   ACTIVE
   4  6607   3670  85.0     .5      11.7     .3     .2   17.2    4.9     0
1  DPY   ACTIVE
  17  6607   3145  23.8     .0       5.4     .0     .0    4.0    5.9     0
2  DPY   ACTIVE
   <snip>
  23  6714  17548  18.6     .1      56.9     .1     .0   66.8   37.4     0
3
  24  6714  17548  18.6     .2      67.6     .1     .0   76.6   50.2     0
3


What could I expect if we lost either drive 23 or 24?  Can the system ride
out the loss of a user ASP?  If not, and it crashes, when the failed disk
is replaced and the system is brought back up, is there any data loss in
the ASPs that *are* RAID protected? (This is a V4R4 system).

Scott Lindstrom
   
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