Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sat, 29 Aug 2009 07:28:21 -0400 | From | Ric Wheeler <> | Subject | Re: [testcase] test your fs/storage stack (was Re: [patch] ext2/3: document conditions when reliable operation is possible) |
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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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