On 25/11/13 03:14, Russell Coker wrote: > On Mon, 25 Nov 2013, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: >>> If that is the problem then the solution would be to just enable >>> read-ahead. Don't we already have that in both the OS and the disk >>> hardware? The hard- drive read-ahead buffer should at least cover the >>> case where a seek completes but the desired sector isn't under the >>> heads. >> >> I'm not sure if read-ahead would solve such a problem, if indeed this is >> a possible problem. AFAIK the RAID5/6 drivers process stripes serially, >> not asynchronously, so I'd think the rebuild may still stall for ms at a >> time in such a situation. > > For a RAID block device (such as Linux software RAID) read-ahead should work > well. For a RAID type configuration managed by the filesystem where you might > have different RAID levels in the same filesystem it might not be possible. > > It would be a nice feature to have RAID-0 for unimportant files and RAID-1 or > RAID-6 for important files on the same filesystem. But that type of thing > would really complicate RAID rebuild. > I think btrfs is planning to have such features - different files can have different raid types. It certainly supports different raid levels for metadata and file data. But it is definitely a feature you want on the filesystem level, rather than the raid block device level. -- 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
