Re: ext3 journal on software raid (was Re: PROBLEM: Kernel 2.6.10 crashing repeatedly and hard)

On Tuesday January 4, andy@strugglers.net wrote:

On Tue, Jan 04, 2005 at 01:22:56PM +1100, Neil Brown wrote:

quoted

On Monday January 3, ewan.grantham@gmail.com wrote:

quoted

I've setup a RAID-5 array using two internal 250 Gig HDs and two
external 250 Gig HDs through a USB-2 interface. Each of the externals
is on it's own card, and the internals are on seperate IDE channels.

I "thought" I was doing a good thing by doing all of this and then
setting them up using an ext3 filesystem.

Sounds like a perfectly fine setup (providing always that external
cables are safe from stray feet etc).

No need to change anything.

Except that Peter says that the ext3 journals should be on separate
non-mirrored devices and the reason this is not mentioned in any
documentation (md / ext3) is that everyone sees it as obvious.
Whether it is true or not it's clear to me that it's not obvious to
everyone.

If Peter says that, then Peter is WRONG.

ext3 journals are much safer on mirrored devices than on non-mirrored
devices just the same as any other data is safer on mirrored than on
non-mirrored. 
In the case in question, it is raid5, not mirrored, but still raid5 is
safer than raid0 or single devices (possibly not quite as safe was raid1).

NeilBrown