[lug] LVM on RAID on Ubuntu

[Sean Reifschneider]

Zan Lynx wrote:
 > Swap isn't that bad...

How so?  DRAM has an average access latency of around 10ns, a hard drive is
10ms, so if you're really using swap to the extent that the performance of
it being on LVM is an issue, you're almost certainly seeing a thousand fold
drop in system performance, leading to a situation we call "thrashing".

Yes, if you are using swap very lightly, just to store unused trash in, you
aren't in that situation because you aren't relying on the performance of
swap.  In which case, LVM overhead really doesn't come into play.

 > In your case, I would create a swap partition on each disk and assign
 > them both as swap with the same priority level.  That gives you
 > basically RAID-0 swap.

It depends on what your goal is, but I always put swap on RAID-1.  Because
I usually want my system to continue operating through a disc failure, and
if swap becomes unavailable due to a disc failure that's going to make the
system go away.  But, if you aren't concerned about system availability, just
data replication, then having multiple swap partitions is the way to go.

Sean
-- 
Sean Reifschneider, Member of Technical Staff <jafo at tummy.com>
tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability