On 2017/9/15 下午4:27, Shaohua Li wrote: > This is a short note based on Song's record. Please reply to the list if > anything is missing. [snip] > > *stream ID > Support stream ID in MD. It should be fairly easy to support stream ID in > raid0/1/10. Intel guys described a scenario in raid5 which breaks stream ID, > eg, write stripe data multiple times because of read-modify-write (clarify?). > Probably detecting IO pattern like what DM does can help. > Can anyone give me a hint what is stream ID in the context of md raid ? > *split/merge problem > md layer splits bio and block layer will do bio merge for low level disks. The > merge/split overhead is noticeable for raid0 with fast SSD and small chunk > size. Fixing the issue for raid0 is doable. Fixing for raid5 is not sure. > Discussed increasing stripe size of raid5 to reduce the split/merge overhead. > There is tradeoff here for example more unnecessary IO for read-modify-write > with bigger stripe size. > > *Testing > md need recover data after disk failures, mdadm has test suite, but not > covering all cases. mdadm test suite is fragile, may kill the machine > We need to build more completed tests. > > The recent null_blk block device driver can emulate several types of disk > failures. The plan is to make null_blk support all disk failures which md can > handle and create a test suite using null_blk. Help is welcome! > > *RAID-1 RAID-10 barrier inconsistency > Coly improved the barrier scalibility for raid1, hopefully he can do the same > for raid10 > Copied, I will handle it. > *DAX > Support DAX in raid0/linear should not be hard. Does it make sense to support > other raid types? > > *sysfs / ioctl > Jes started working on it. Goal is to replace ioctl with sysfs based interfaces. > There are gaps currently, eg, some operations can only be done with ioctl. Suse > guys promised to close the gap in kernel side. > Yes, I will handle kernel part. The change will be done one by one, step by step. The first step is to unify code path for both ioctl and sysfs interfaces. Once I finish my emergent tasks on hand, I will start to handle this. Hopefully this work can start by end of this year. > Using configfs instead of sysfs? > Currently it is sysfs and I feel is it OK being sysfs interface. Do we have specific reason or benefit for using configfs ? Thanks for the informative notes, thank you all for the discussion ! Coly Li -- 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
