Tuesday, July 1, 2008

Let ZFS manage even more space more eficiently

The idea of using ZFS to manage process core dumps begs to be expanded to at least crash dumps. This also enters into the realm of Live Upgrade as it eliminates the need to sync potentially a lot of data on activation of a new BE!

Previously I created a ZFS file system in the root pool, and mounted it on /var/cores.

The same purpose would be even better served with a generic ZFS file system which can be mounted on any currently active Live-Upgrade boot environment. The discussion here suggests the use of a ZFS file system rpool/var_shared, mounted under /var/shared. Directories such as /var/crash and /var/cores can then be moved into this shared file system.


/ $ pfexec ksh -o vi
/ $ zfs create rpool/var_shared
/ $ zfs set mountpoint=/var/shared rpool/var_shared
/ $ mkdir -m 1777 /var/shared/cores
/ $ mkdir /var/shared/crash
/ $ mv /var/crash/`hostname` /var/shared/crash

View my handiwork:

/ $ ls -l /var/shared

total 6
drwxrwxrwt   2 root     root           2 Jun 27 17:11 cores
drwx------   3 root     root           3 Jun 27 17:11 crash
/ $ zfs list -r rpool
NAME                       USED  AVAIL  REFER  MOUNTPOINT
rpool                     13.3G  6.89G    44K  /rpool
rpool/ROOT                10.3G  6.89G    18K  legacy
rpool/ROOT/snv_91         5.95G  6.89G  5.94G  /.alt.tmp.b-b0.mnt/
rpool/ROOT/snv_91@snv_92  5.36M      -  5.94G  -
rpool/ROOT/snv_92         4.33G  6.89G  5.95G  /
rpool/dump                1.50G  6.89G  1.50G  -
rpool/export              6.83M  6.89G    19K  /export
rpool/export/home         6.81M  6.89G  6.81M  /export/home
rpool/swap                1.50G  8.38G  10.3M  -
rpool/export/cores          20K  2.00G    20K  /var/cores
rpool/var_shared            22K  3.00G    22K  /var/shared

Just to review the current settings for saving crash dumps:

/ $ dumpadm

      Dump content: kernel pages
       Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
Savecore directory: /var/crash/solwarg
  Savecore enabled: yes

Set it to use the new path I made above:

/ $ dumpadm -s /var/shared/crash/`hostname`

      Dump content: kernel pages
       Dump device: /dev/zvol/dsk/rpool/dump (dedicated)
Savecore directory: /var/shared/crash/solwarg
  Savecore enabled: yes

Similarly I update the process core dump settings:

/ $ coreadm -g /var/shared/cores/core.%z.%f.%u.%t
/ $ coreadm

     global core file pattern: /var/shared/cores/core.%z.%f.%u.%t
     global core file content: default
       init core file pattern: core
       init core file content: default
            global core dumps: disabled
       per-process core dumps: enabled
      global setid core dumps: enabled
 per-process setid core dumps: disabled
     global core dump logging: enabled

And finally, some cleaning up:

/ $ zfs destroy rpool/export/cores
/ $ cd /var
/var $ rmdir crash
/var $ ln -s shared/crash
/var $ rmdir cores

As previously, the above soft link is just in case somewhere there is a naughty script or tool with a hard coded path to /var/crash/`hostname`. I don't expect to find something like that in oficially released Sun software, but I do some times use programs not officially released or supported by Sun.

This makes me wonder what else can I make it do! I'm looking forward to my next Live Upgrade to see how well it preserves my configuration before I attempt to move any of the spool directories from /var to /var/shared!

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