Thanks to George Guethlein, Allan Rollow, Alan Davis for their answers on this
one.
>From George
1) I found that system maintenance is easier if ALL system related "stuff" is
in rootdg. This is the one diskgroup LSM is totally aware of, as it must exist
if you use LSM. You don't really need swap2 in another (or it's own )
diskgroup. It's not like you would ever do a "voldgexport/import" on it. Also,
if you ever need to cluster your system in the future, you will be in a good
position already.
My personal preferrence is to kepp all O/S related filesystems, etc., in rootdg.
2) You should be able to remove one half of the mirrors from the LSM swap2
volumes. The following outline assumes the disks are completely used for LSM
swap2 volume:
Stop the mirror volume, disassociate the plexes and remove the subdisks
Remove the disk entries from the OLD diskgroup
Add the disks to rootdg
Make the new swap2 volume (same as current - same name is OK since it's
in a different diskgroup)
LSM manual for DUnix 4.0 or Higher (section 7-9, page7-23) - DO NOT
STRIPE IT
Go to single-user mode
Change the fstab entry to point to the new LSM swap2 volume
Boot the system
You may be able to use "swapon" to allocate the NEW swap2 as swap
space
But, it won't be mirrored, & you can't get to the other disks until
you cycle the O/S
Verify new LSM volume is being used
Stop the OLD volume, disassociate the plexes and remove the subdisks
Remove the disk entries from the OLD diskgroup
If these are the last disks in the diskgroup, you'll have to export it
first to get them all out
Then, **I think** reinitialize them in rootdg
Add the disks to rootdg
Setup the mirror subdisks & plexes and attach them to the new swap2 volume
LSM manual for DUnix 4.0 or Higher (section 7-9, page7-23)
3) The text in LSM manual for DUnix 4.0 or Higher (section 7-9, page7-23)
states:
"If you are adding multiple disks as LSM volumes to secondary swap, add the
disks as several
individual LSM volumes rather than striping or concatenating them into a
single, larger LSM
volume. Adding multiple LSM volumes is preferrable because the swapping
algorithm
automatically distributes its data across multiple disks to improve
performance."
You don't want add the additional overhead of the striping algorithm.
>From Allan Rollow
Your first question was asked in the last few months on the list,
I think. The summary should be in the archive.
LSM provides lots of commands for managing it. Look through
the manual pages to see if there is a command that can change
the disk group of a device. If not, you'll probably have to
stop using the swap space, delete the volume, plexes, device
and add them back in rootdg.
As for the configuration, the striping should provide a higher
performance page/swap device and the mirroring will make it
more resistent to I/O errors. The striping performance will
be senstive to how the disks are spread out over available
controllers. If all the disks are on one or two controllers
there won't be much performance value for high bandwidth loads.
Of course, if you rarely page and only need the swap space to
support a large amount of virtual memory, the performance isn't
very relevant. An 8 GB add-on page/swap space in conjunction
with the typical primary page/swap space will create an imbalance
in how space is allocated, but the striping will help even that
out.
>From Alan Davis
Only rootdg is available at boot time for the system to properly recognise
encapsulated swap. Only rootdg partitions can be used as dumpdev. Only
rootdg cannot be exported (exporting a swap partition while it's in use is
considered bad form).
There are other considerations as well, most notably that swap must be on
lun0 devices only.
The original questions
Gwen Pettigrew wrote:
>
> Hi All
> I have a few questions about using secondary swap space and LSM.
>
> On one of the systems I look after we have a 8 GB swap partition under LSM. The
> secondary swap has been placed in its own disk group. The LSM docs say that
> secondary swap should be place in the rootdg disk group. The OS we are using is
> 4.0B, and the hardware is a 8400.
>
> My questions are;
> 1) What are the reasons for having the secondary swap in the rootdg group?
>
> 2) What is best way of going about moving the secondary swap to the rootdg?
>
> 3) At the moment the secondary swap consists of 2 * 8 GB mirrored plexes. Each
> plex has four disks which are striped. Is this the best way of providing
> secondary swap or is some other strategy more suitable?
--
Gwen Pettigrew
Computer Officer
Institute of Theoretical Geophysics
Department of Earth Sciences
Downing Street
Cambridge
CB2 3EQ
UK
Tel 01223 333464
E-mail gwen_at_itg.cam.ac.uk
W3 http://www.itg.cam.ac.uk/ITG/members/gwen/
Received on Thu Jun 10 1999 - 08:50:18 NZST