On Fri, Sep 15, 2017 at 10:42:23PM +0200, Coly Li wrote: > 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 ? I think it's called write hint right now, see c75b1d9421f8 fs: add fcntl() interface for setting/getting write life time hints > > > *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 ? No strong reason, just because configfs is generally for configure. If sysfs works here, I think it's ok. Thanks, Shaohua -- 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
