ITEM: BQ2794L

How does sysback create the size rootvg's vgda

Question:

Env:
  AIX 4.1.4
  RISC R40
  sysback 3.3.3.8

Desc:
  Customer does a install from a sysback tape on to one 
  4.5gb disk for rootvg.  Then he tries to extend rootvg 
  by one  more 4.5gb one week later.  He gets the error 
  that he ran out of descriptor space.  On a idenitcal 
  system he uses mksysb and only installed onto one 4.5gb
  disk.  One week later he is able to add another 4.5gb disk 
  with out problems.
  Why does mksysb work, but not sysback?

Action:
  Looking at the mksysb code /usr/lpp/bosinst/bi_main 
  Here is what they do:

        TOTAL_TARGETS=`bidata -G | wc -l`
        \# If TOTAL_TARGETS is null, put the number 1 in there.
        TOTAL_TARGETS=${TOTAL_TARGETS:-1}
        \# Add 7 to TOTAL_TARGETS to ensure that the lvm will allow at least 8
        \# disks to be put into the rvg.
        (( MAXPVS = TOTAL_TARGETS + 7 ))

        \# if this is an 8 meg machine, turn off the datadaemon
        \# durning mkvg. Reduce maxpvs by 4.
        if [ "$REALMEM" -le 8192 ]
        then
                bidata -wx
                (( MAXPVS = MAXPVS - 4 ))
    then
                bidata -wx
                (( MAXPVS = MAXPVS - 4 ))
        fi

        mkvg -f -y $VG -s $PPS -d $MAXPVS $DISKS; rc=$?

So they increase the number of disk by 7.  So if the 
customer selects 2 drives to install on the mksysb the 
MAXPVS will be set to 9.  So the vgda will then be 
9 * 1016.

However sysback will set the maxpvs to the total number of disk selected.
This has caused some serious issues with customer's adding another disk
to rootvg in the future.  In most of the cases the customer needed to add 
the disk to rootvg and could not just create another vg with that disk.

We can do two possible things.  
1.  Increase maxpvs by some value 2,3,4,5 (whatever)
2.  Leave it as a option in the edit vg menu

I do realize we have a limited amount of ram filesystem 
and why this process is that way.

Sysback used to always multiply the number of disks by 
two before creating rootvg, but I now see it's no longer 
doing this. I have no idea where this code went or when. 
I will reapply the change, but for consistency will also 
increase by 7 instead. This will be included in 
sysback 3.3.3.10

Next Action:
  Sending sysback 3.3.3.10 to the customer
  Closing with customer approval



Support Line: How does sysback create the size rootvg's vgda ITEM: BQ2794L

Dated: November 1996 Category: N/A

This HTML file was generated 99/06/24~13:30:20

Comments or suggestions?
Contact us