On 08/29/2009 05:49 AM, Pavel Machek wrote:
So instead of fixing or at least documenting known software deficiency
in Linux MD stack, you'll try to surpress that information so that
people use more of raid5 setups?
Perhaps the better documentation will push them to RAID1, or maybe
make them buy an UPS?
people aren't objecting to better documentation, they are objecting to
misleading documentation.
Actually Ric is. He's trying hard to make RAID5 look better than it
really is.
I object to misleading and dangerous documentation that you have
proposed. I spend a lot of time working in data integrity, talking and
writing about it so I care deeply that we don't misinform people.
In this thread, I put out a draft that is accurate several times and you
have failed to respond to it.
The big picture that you don't agree with is:
(1) RAID (specifically MD RAID) will dramatically improve data integrity
for real users. This is not a statement of opinion, this is a statement
of fact that has been shown to be true in large scale deployments with
commodity hardware.
(2) RAID5 protects you against a single failure and your test case
purposely injects a double failure.
(3) How to configure MD reliably should be documented in MD
documentation, not in each possible FS or raw device application
(4) Data loss occurs in non-journalling file systems and journalling
file systems when you suffer double failures or hot unplug storage,
especially inexpensive FLASH parts.
ric
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