On Sun, Jan 02, 2005 at 09:18:13PM +0100, Peter T. Breuer wrote: > Stephen Tweedie wrote: > > Umm, if soft raid is expected to have silent invisible corruptions in > > normal use, > > It is, just as is all types of RAID. This is a very strange thing for > Stephen to say - I cannot believe that he is as naive as he makes > himself out to be about RAID here and I don't know why he should say > that (presuming that he really knows better). > > > then you shouldn't be using it, period. That's got zero to > > do with journaling. > > It implies that one should not be doing journalling on top of it. > > (The logic for why RAID corrupts silently is that errors accumulate at > n times the normal rate per sector, but none of them are detected by > RAID (no crc), and when a disk drops out then you get a good chance of > picking up a corrupted copy instead of a good copy, because nobody > has checked the copy meanwhiles to see if it matches the original). I have no idea which of you to believe now. :( I currently only have one system using software raid, and several of my employer's machines using hardware raid, all of which have various raid-1, -5 and -10 setups and all use only ext3. Let's focus on the personal machine of mine for now since it uses Linux software RAID and therefore on-topic here. It has /boot on a small RAID-1, and the rest of the system is on RAID-5 with an additional RAID-0 just for temporary things. There is nowhere that is not software RAID to put the journals, so would you be recommending that I turn off journalling and basically use it as ext2? What I do know is that none of what you say is in the software raid howto, and if you are right, it really should be. Neither is it in any ext3 documentation and there is no warning on any distribution installer I have ever used (those that understand RAID and LVM and are happy to set that up at install time with ext3). Also everyone that I have spoken to about this knows nothing about it, so what you are saying, if correct, would seem to have far-reaching implications.
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