Just to complicate things, consider this setup:
# cat /proc/swaps
Filename Type Size Used Priority
/dev/md5 partition 999864 16904 0
/dev/md6 partition 999864 16924 0
/dev/md7 partition 999864 16920 0
Those are all RAID-1 mirrors, a measure whose ass-saving value I have
enjoyed.
While a crash dump to just half of one of those mirrors is fine, finding it
might be a little bit tricky. And the fact that the kernel reassembles
the mirrors automatically on boot might make retrieving the data a little
bit tricky, too.
(After a crash, the mirrors will be inconsistent, so one will get copied
over the other, but I'm not too clear on which direction it'll happen in.)
I can't NOT reassemble at least some mirrors on boot because / is mirrored!
Now, to that, add the case that each of those is significantly smaller than
main memory. (2/3 size would still allow swap = 2*ram.)
The problem is that hardware is getting more and more sopisticated and
requiring ever more elaborate device drivers. Eventually you have to
have a cutoff and say that something is too complex to talk to after a
crash, even though it's theoretically available. Where is that line?
USB? iSCSI? This situation?
A reasonable fallback is to just drop in a cheap crappy dedicated
IDE drive for catching crash dumps, but I'd like the crash dumper to
know how to wake it up from sleep mode; I'd hate to leave it spinning
all the time...
On Sun, Nov 03, 2002 at 05:08:23PM -0000, [email protected] wrote:
> Just to complicate things, consider this setup:
>
> # cat /proc/swaps
> Filename Type Size Used Priority
> /dev/md5 partition 999864 16904 0
> /dev/md6 partition 999864 16924 0
> /dev/md7 partition 999864 16920 0
>
> Those are all RAID-1 mirrors, a measure whose ass-saving value I have
> enjoyed.
>
> While a crash dump to just half of one of those mirrors is fine, finding it
> might be a little bit tricky. And the fact that the kernel reassembles
> the mirrors automatically on boot might make retrieving the data a little
> bit tricky, too.
>
> (After a crash, the mirrors will be inconsistent, so one will get copied
> over the other, but I'm not too clear on which direction it'll happen in.)
>
> I can't NOT reassemble at least some mirrors on boot because / is mirrored!
>
> Now, to that, add the case that each of those is significantly smaller than
> main memory. (2/3 size would still allow swap = 2*ram.)
You would want a dump2disk that could span devices.
Probably a module that would put a header on each part with
a dumpID and sequence#. Compression would also help here as
well. The right compression would actually accelerate the
process.
Early userspace would locate and assemble the pieces and put
the dump somewhere. This might happen between mounting /
and assembling the other mirrors. That would be up to you.
--
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J.W. Schultz Pegasystems Technologies
email address: [email protected]
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