Increasing size of System Dumpdeivice

Overview

When an unexpected system halt occurs, the system dump facility automatically copies selected areas of kernel data to the primary dump device. These areas include kernel segment 0, as well as other areas registered in the Master Dump Table by kernel modules or kernel extensions. An attempt is made to dump to a secondary dump device if it has been defined.
When you install the operating system, the dump device is automatically configured for you. By default, the primary device is /dev/hd6, which is a paging logical volume, and the secondary device is /dev/sysdumpnull.
Note:
If your system has 4 GB or more of memory, then the default dump device is /dev/lg_dumplv, and is a dedicated dump device.


If a dump occurs to paging space, the system will automatically copy the dump when the system is rebooted. By default, the dump is copied to the/var/adm/ras directory in the root volume group. See the sysdumpdev command for details on how to control dump copying.

sometimes we get an error like “Largest Dump Device is too small”

Checking for the current dump device

Get the size of the current dump devices:
sysdumpdev -l
Example:
nlasltp2@/home/a124037>sudo sysdumpdev -l
primary /dev/hd7
secondary /dev/hd7x
copy directory /var/adm/ras
forced copy flag TRUE
always allow dump TRUE
dump compression OFF

Get the estimate of the size needed for the dumpdevice:

sysdumpdev –e
Example:
nlasltp2@/home/a124037>sudo sysdumpdev -e
0453-041 Estimated dump size in bytes: 5002756096



Check the size of the current dump devices (based on the primary and secondary from the sysdumpdev -), the dump device will most likely be found on the rootvg:

nlasltp2@/home/a124037>lsvg -l rootvg
rootvg:
LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT
hd5 boot 1 2 2 closed/syncd N/A
hd6 paging 90 180 2 open/syncd N/A
hd8 jfslog 1 2 2 open/syncd N/A
hd4 jfs 1 2 2 open/syncd /
hd2 jfs 21 42 2 open/syncd /usr
hd9var jfs 2 4 2 open/syncd /var
hd3 jfs 4 8 2 open/syncd /tmp
hd1 jfs 1 2 2 open/syncd /home
hd10opt jfs 1 2 2 open/syncd /opt
appllv jfs 1 2 2 open/syncd /appl
tsulv jfs 2 4 2 open/syncd /appl/tsu
esmlv jfs 2 4 2 open/syncd /appl/esm
operflv jfs 1 2 2 open/syncd /appl/sptools/operf
sptoolslv jfs 4 8 2 open/syncd /appl/sptools
hd7 sysdump 19 19 1 open/syncd N/A
hd7x sysdump 19 19 1 open/syncd N/A
hascriptlv jfs 2 4 2 open/syncd /appl/ha-scripts
tivlv jfs 4 8 2 open/syncd /appl/Tivoli

From the example you can see that hd7 is using 19 PP (the same for hd7x). They should be on different disks and you might like to check that at this time although it is unrelated to the size (on different disks such that the dump is available if a disk fails). This can be checked by the following commands:

nlasltp2@/home/a124037>lslv -m hd7
hd7:N/A
LP PP1 PV1 PP2 PV2 PP3 PV3
0001 0092 hdisk0
0002 0093 hdisk0
0003 0094 hdisk0
0004 0095 hdisk0
0005 0096 hdisk0
0006 0097 hdisk0
0007 0098 hdisk0
0008 0099 hdisk0
0009 0100 hdisk0
0010 0101 hdisk0
0011 0102 hdisk0
0012 0103 hdisk0
0013 0104 hdisk0
0014 0105 hdisk0
0015 0106 hdisk0
0016 0107 hdisk0
0017 0108 hdisk0
0018 0109 hdisk0
0019 0110 hdisk0
nlasltp2@/home/a124037>lslv -m hd7x
hd7x:N/A
LP PP1 PV1 PP2 PV2 PP3 PV3
0001 0092 hdisk2
0002 0093 hdisk2
0003 0094 hdisk2
0004 0095 hdisk2
0005 0096 hdisk2
0006 0097 hdisk2
0007 0098 hdisk2
0008 0099 hdisk2
0009 0100 hdisk2
0010 0101 hdisk2
0011 0102 hdisk2
0012 0103 hdisk2
0013 0104 hdisk2
0014 0105 hdisk2
0015 0106 hdisk2
0016 0107 hdisk2
0017 0108 hdisk2
0018 0109 hdisk2
0019 0110 hdisk2

(The increase procedure is based on the above example)

Increasing the size of the Dump device


PP size in the example was 128 MB. 19 PPs was used which gives us 2432 MB current dump device. Compare that to the estimated of 5002756096 which is roughly 5000MB. This is 40+PP so select 44 (~10% extra) for growth. Thus we need to increase with 44-19= 25PPs for each of the logical volumes. In our case this is fine as we have 778 PPs free (make sure there are at least 200 more free in addition to this, otherwise escalate as the PP might be needed for more urgent matters). Thus we increase each of the LVs (and it is pure 25PP as they are not mirrored):
extendlv hd7 25
extendlv hd7x 25