Increasing swap space

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Date: Thu, 20 Nov 2003 11:47:43 +1300
To: "'tru64-unix-managers@ornl.gov'" <tru64-unix-managers@ornl.gov>

Hi managers,

The DS20E server (1GB RAM, 2CPUs, Tru64v5.1B) that we look after is short on
memory
and the customer wants to add 3GB RAM (to have 4GB total). At the moment the
server
has 3GB swap space, so we should probably increase that as well.

As far as we know, the recommended swap size for Tru64 is 2.5-3 * RAM if the
swap
allocation mode is 'eager' and at least 1*RAM if the swap mode is 'lazy'. Is
it
a problem if the system has more RAM than swap space (if we leave the swap
space
size at 3GB and have 4GB RAM)? If that is not going to cause any problems,
we would
probably wait for some time and monitor swap usage to see if they really
need more
swap space on that server.

Increasing swap space size could be quite complicated here. What worries us
is
that the server has 4*72GB disks all in one RAID 1+0 (the system was
originally
configured by HP). Here is the output of the disklabel command:

8 partitions:
# size offset fstype fsize bsize cpg # ~Cyl values
  a: 2097152 0 AdvFS # 0 - 511
  b: 6588334 2097152 swap # 512 -
2120*
  c: 284524544 0 unused 0 0 # 0 -
69463
  d: 94317226 1572864 unused 0 0 # 384 -
23410*
  e: 94317226 95890090 unused 0 0 # 23410*-
46437*
  f: 2695515 281829029 AdvFS # 68805*-
69463
  g: 11979980 269849049 AdvFS # 65881*-
68805*
  h: 261163563 8685486 AdvFS # 2120*-
65881*

where partition a is 'root_domain', b is swap, f is 'tmp_domain', g is
'usr_domain'
and h is 'app01_domain'.

Our idea was to take some space from the h partition and either add it to
partition b
(if possible), or to make one of the unused partitions (d or e) as another
swap
partition using that extra space from partition h. That would include the
following
steps:

- make full filesystem backup
- save current disklabel (disklabel -r dsk0 > /tmp/dsk0label)
- unmount filesystems in app01_domain and remove that file domain
- edit /tmp/dsk0label - shrink partition h and extend partition b (if
possible)
                        or create new swap partition using d or e.
- create a new disk label for dsk0 (disklabel -R dsk0 /tmp/dsk0label)
- create app01_domain and filesets, mount filesystems in app01_domain
- restore data to the filesystems in app01_domain

QUESTIONS:

- is this procedure OK?
- can we be sure that if we are changing only partitions b and h nothing
else would
  be affected by the 'disklabel -R' command (especially not the
root_domain!!!)?
- can the partition b be increased while it is in use
  (or should it be done in single user mode)?
- is it better to create new swap partition, rather than to resize partition
b
  (it shouldn't cause performance problems as it's all striped anyway)?
- do we need to specify -r and -t options with 'disklabel -R' command to
make
  sure that the disk will be bootable (although it already is)?
- what do we need to change in the /etc/fstab and /etc/sysconfigtab if we
create
  a new swap partition?
- is it a problem to have more RAM than swap space (e.g. in case the
application
  reserves the same amount of swap space as the real memory, or for memory
dump)?
- any other suggestions?

Thanks in advance,
Zoran

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