Question

[Mike_305]

Hi,

When you mirror root, do you have to mirror dump in case of if we have swap and dump configured separately. Where swap is not as swap + dump. I have two questions.

What happens to dump device if the primary disk fails and you boot from alternate?

Also, what happens when you change the primary disk, do you get your dump device back on to the new disk?

Thanks in advance.

Thanks

[Duncan Edmonstone]

As I understand it if you have dump configured sperate to swap theres not much point in mirroring dump, as dump is just written out from a certain offset, and pays no attention to LVM structures.

You should, of course mirror swap though.

HTH

Duncan

[A. Clay Stephenson]

When you mirror dump (or dump is also primary swap and is mirrored), it is literally a crap shoot as to where the dump actually goes. It will be written to only one of the disks. For this reason, I prefer to configure a very small (256-512MB primary swap that is mirrored) and then a separate unmirrored dump area or areas.

[Mike_305]

Hi Guys,

After booting from alternate if it needs to perform dump, where it will dump the data?

Remember alternate disk doesen't have dump area mirror from primary.

Thanks.

[MANOJ SRIVASTAVA]

Hi

You have to make the the mirror disk the same as the primar root disk wiht swap , and dump partitions as defined , in case you want the system to come up happily if the primary disk fails.


Manoj Srivastava

[S.K. Chan]

In my opinion you should stick to having your primary swap being the dump LV also when you mirror your root disk. It is only if you feel that you need additional dump space (bare in mind for a full system crash dump you need at least the same amount of dump space as your physical memory). You can find out how much dump you need with ..
# crashconf -v
===> only on 11.x
For example I have "lvol9" setup as additional dump space (from "lvlnboot -v")

Physical Volumes belonging in Root Volume Group:
/dev/dsk/c3t6d0 (52.6.0) -- Boot Disk
Boot: lvol1 on: /dev/dsk/c3t6d0
Root: lvol3 on: /dev/dsk/c3t6d0
Swap: lvol2 on: /dev/dsk/c3t6d0
Dump: lvol2 on: /dev/dsk/c3t6d0, 0
Dump: lvol9 on: /dev/dsk/c3t5d0, 1

Having said that, I think the answer to your question is it'll simply failed to dump since it could find any dump space, you'll see error like ..

Warning: insufficient space on dump device to save full crashdump.

[Michael Tully]

Hi,

Mirroring dump is *essential* if it is on your
root disk pairing, because if your primary disk
fails where is your dump going to go?

In saying that having a small primary swap is
far better for system performance. I generally
use secondary swap areas that shares dump and
depending on the setup for each server it will
most likely end up on a disk array whether it
attached directly or through a switch.

Cheers
~Michael~