Wilson Wilson wrote: > Neil great stuff, its online now!!! Congratulations :) > > I am still unsure how this raid5 volume was partially readable with 4 > disks missing. My understanding each file is written across all disks > apart from one, which is used for CRC. So if 2 disks are offline the > whole thing should be unreadable. I'll try :) md doesn't operate at a file level, it operates on chunks. The chunk could be 64Kb in size. For raid5 each stripe is made of n-1 chunks. (raid6 would be n-2). When a stripe is read, if your file is in one of the chunks that's still there then you're in luck. I guess md knows it's degraded and gives as much data back as possible. This means that you have a certain probability of accessing a given file depending on it's size, the filesystem and the degree to which the array is degraded. FWIW I'd *never* try a r/w operation on such a degraded array. Speculation: I'm surprised you could mount such a 'sparse' array though. I wonder if some filesystems (like xfs) would just barf as they mounted because they have more distributed mount-time data structures and would spot the missing chunks. Others (ext3?) may just mount and try to read blocks on demand. David - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
