On 30/11/17 10:26, Duane wrote: > Why is the data offset set so big? I created a 3x4TB RAID5 array and the > data offset was 128MB. Chunk size was the default 512kB. > > I cannot see why such a large offset is used. I would think the data > offset need only be at most the chunk size plus the space (1 sector) for > the superblock and bitmap. > > When reshaping the array, I am prompted to use an external file, so I > don't see that mdadm ever uses the space. > Do you mean the manual tells you, or that mdadm refuses to run otherwise? Certainly with a new array on larger disks, a backup file should be totally unnecessary. Run a reshape of some sort, and see if the offset changes :-) > > I tried making some test arrays and got much smaller sizes. A 3x1GB > RAID5 array with 64k chunks had a 1MB data offset. > > > If I make a 7x4TB RAID5 array with 64kB chunks, is there a problem with > setting the data offset to around 2MB? > Dunno. How do you know the bitmap is "just one block"? I haven't dug in to it so I don't know, but it makes sense to me that as the disks get bigger, so does the bitmap. What's the point of fighting the defaults, anyway? Just add another/bigger disk if you need more space. Cheers, Wol -- 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
