On Oct 22, 2013, Brendan Hide <bren...@swiftspirit.co.za> wrote: > On 2013/10/22 07:18 PM, Alexandre Oliva wrote: >> ... and >> it is surely an improvement over the current state of raid56 in btrfs, >> so it might be a good idea to put it in. > I suspect the issue is that, while it sortof works, we don't really > want to push people to use it half-baked.
I don't think the current state of the implementation upstream is compatible with that statement ;-) One can create and run a glorified raid0 that computes and updates parity blocks it won't use for anything, while the name gives the illusion of a more reliable filesystem than it actually is, and it will freeze when encountering any of the failures the name suggests it would protect from. If we didn't have any raid56 support at all, or if it was configured separately and disabled by default, I'd concur with your statement. But as things stand, any improvement to the raid56 implementation that brings at least some of the safety net raid56 are meant to provide makes things better, without giving users an idea that the implementation is any more full-featured than it currently is. > Maybe it would be nice to have some half-baked code *anyway*, > even if Chris doesn't put it in his pull requests juuust yet. ;) Why, sure, that's why I posted the patch; even if it didn't make it to the repository, others might find it useful ;-) >> So far, I've put more than >> 1TB of data on that failing disk with 16 partitions on raid6, and >> somehow I got all the data back successfully: every file passed an >> md5sum check, in spite of tons of I/O errors in the process. > Is this all on a single disk? If so it must be seeking like mad! haha Yeah. It probably is, but the access pattern for most of the time is mostly random access to smallish files, so that won't be a problem. I considered doing raid1 on the data, to get some more reliability out of the broken disk, but then I recalled there was this raid56 implementation that, in raid6, would theoretically bring about additional reliability and be far more space efficient, so I decided to give it a try. Only after I'd put in most of the data did the errors start popping out. Then I decided to try and fix them instead of moving data out. it was some happy hacking ;-) -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
